ExamFinch.com My Study

Study guide

Windows OS Troubleshooting

Practice this exam

CompTIA A+ 220-1201 & 220-1202

Track your progress as you read

Finished sections get a check mark.

1 Introduction & Exam Overview

About the CompTIA A+ Certification Exam Domains & Study Strategy

2 Core 1 Domain 1: Mobile Devices (13%)

Laptop Hardware & Components Laptop Features & Display Types Mobile Device Connectivity & Accessories Mobile Operating System Features Mobile Device Synchronization & Data Transfer

3 Core 1 Domain 2: Networking (23%)

TCP/IP Fundamentals & the OSI Model Common Ports & Protocols Wireless Networking Standards Network Hardware & Devices Network Configuration & Internet Connections Network Types & Topologies

4 Core 1 Domain 3: Hardware (25%)

Cables & Connectors RAM Types & Storage Devices Motherboards, CPUs & Power Supplies Printers & Multifunction Devices Peripheral Devices & Expansion Cards Network Cable Tools & Testing

5 Core 1 Domain 4: Virtualization & Cloud Computing (11%)

Virtualization Concepts Cloud Computing Models & Services Client-Side Virtualization in Practice

6 Core 1 Domain 5: Hardware & Network Troubleshooting (28%)

CompTIA Troubleshooting Methodology Hardware Troubleshooting Network Troubleshooting Printer Troubleshooting Display & Mobile Device Troubleshooting

7 Core 2 Domain 1: Operating Systems (28%)

Windows Editions & Features Windows Administrative Tools & Utilities Windows Command Line & PowerShell macOS & Linux Basics Windows Networking & File Sharing Windows Installation & Upgrade Methods

8 Core 2 Domain 2: Security (28%)

Physical & Logical Security Measures Malware Types & Threat Mitigation Wireless & Network Security Encryption & Data Protection

9 Core 2 Domain 3: Software Troubleshooting (23%)

Windows OS Troubleshooting Mobile OS & Application Troubleshooting Browser & Application Troubleshooting

10 Core 2 Domain 4: Operational Procedures (21%)

Documentation & Change Management Backup & Recovery Methods Safety & Environmental Procedures Scripting & Remote Access Technologies Privacy, Licensing & Organizational Policies

Windows OS Troubleshooting

Key Takeaways Explain This Topic AI

A Blue Screen of Death (BSOD) is a kernel-level stop error; record the stop code and any named driver file first, then reboot once before assuming hardware failure.

Safe Mode loads Windows with minimal drivers and services so you can roll back a bad driver, remove malware, or undo a setting that blocks a normal boot.

System Restore reverts system files, the registry, drivers, and installed programs to a restore point but never touches personal files — it is not a backup.

The Windows Recovery Environment (WinRE) offers Startup Repair, System Restore, Command Prompt, System Image Recovery, and Reset this PC when Windows will not boot; trigger it by interrupting boot three times.

On the V15 Core 2 (220-1202) exam, Software Troubleshooting is 23% of objectives and is tested through scenario and performance-based questions — know the CLI repair sequence: DISM /RestoreHealth, then sfc /scannow, plus chkdsk /f /r for disk errors.

Last updated: October 2026

Blue Screen of Death (BSOD)

A Blue Screen of Death (BSOD) , formally a stop error , appears when the Windows kernel hits a fault it cannot safely recover from and halts to protect data on disk. CompTIA expects you to treat the on-screen stop code as the primary diagnostic clue rather than guessing. Modern Windows 10/11 screens show a short code (for example, DRIVER_IRQL_NOT_LESS_OR_EQUAL ) and often the failing driver file name (such as nvlddmkm.sys ), which points directly at the culprit.

Common Stop Codes and Their Real Causes

  • Stop Code Most Likely Cause First Action
  • IRQL_NOT_LESS_OR_EQUAL Bad driver or faulty RAM Roll back driver, run Windows Memory Diagnostic
  • PAGE_FAULT_IN_NONPAGED_AREA Faulty RAM or corrupt driver Test RAM, update driver
  • SYSTEM_SERVICE_EXCEPTION Incompatible driver, corrupt file sfc /scannow, update driver
  • CRITICAL_PROCESS_DIED Corrupt system files or malware sfc, DISM, malware scan
  • DPC_WATCHDOG_VIOLATION Storage/SSD driver timeout Update storage controller driver and firmware
  • UNMOUNTABLE_BOOT_VOLUME Corrupt boot sector, failing drive WinRE → chkdsk C: /f /r
  • INACCESSIBLE_BOOT_DEVICE Changed SATA/RAID mode in firmware Restore prior SATA mode (AHCI/RAID)
  • Worked Triage Sequence

Photograph or write down the stop code and any .sys file named — it is your best first clue.

Reboot once. A lone BSOD can be a transient glitch; do not replace hardware on a single event.

If it repeats , boot to Safe Mode and roll back or uninstall the most recently changed driver (Device Manager → driver → Roll Back Driver).

Run DISM /Online /Cleanup-Image /RestoreHealth (repairs the component store that sfc relies on), then sfc /scannow (repairs protected system files from that store); Microsoft's guidance is to run DISM before sfc.

Run Windows Memory Diagnostic ( mdsched.exe ) if a code points to RAM, and review Event Viewer → Windows Logs → System for the matching error.

Exam trap: Stop codes ending in IRQL or naming a driver are driver/RAM problems, not malware. Reserve malware as the prime suspect for CRITICAL_PROCESS_DIED and unexplained reboots after a download.

Boot Sequence and Startup Repair

Knowing where a boot fails tells you which tool to reach for. The Windows boot order is: POST (hardware self-test) → UEFI/BIOS locates the boot device → Windows Boot Manager (bootmgr) reads the Boot Configuration Data (BCD) → ntoskrnl.exe (kernel) loads drivers → smss.exe (Session Manager) → winlogon.exe presents the sign-in screen. A failure before the spinning logo is usually firmware or BCD; after the logo points to drivers or the user profile.

Boot Symptoms → Fix

  • Symptom Likely Stage Repair
  • "Bootmgr is missing" / "BOOTMGR not found" Boot Manager / BCD WinRE Command Prompt → bootrec commands
  • Spinning dots, never reaches desktop Driver init Safe Mode, roll back recent driver
  • Boot loop before sign-in Kernel/driver or BCD WinRE → Startup Repair, then System Restore
  • Black screen after sign-in explorer.exe / profile Ctrl+Alt+Del → Task Manager → run explorer.exe
  • "Automatic Repair" loop Corrupt files WinRE Command Prompt → sfc, DISM, chkdsk
  • Boot Repair Commands (run from WinRE → Troubleshoot → Command Prompt)
  • Command What It Does
  • bootrec /fixmbr Writes a fresh Master Boot Record (legacy BIOS disks)
  • bootrec /fixboot Writes a new boot sector to the system partition
  • bootrec /rebuildbcd Scans for installs and rebuilds the BCD store
  • sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows Offline system file check when Windows will not boot
  • chkdsk C: /f /r Fixes file-system errors and recovers readable bad sectors

Reach WinRE by holding Shift while clicking Restart, by booting installation media and choosing Repair your computer , or by powering off during boot three times so Windows triggers it automatically. Always try the least-destructive option first — Startup Repair before a reset, and Reset this PC (which can keep files) before a clean reinstall.

  • Safe Mode, Slow Performance, and System Restore
  • Safe Mode

Safe Mode boots Windows with only essential drivers and services, giving you a clean environment to undo whatever blocks a normal boot. There are three variants:

Safe Mode — minimal drivers, basic VGA display, no networking.

Safe Mode with Networking — adds network drivers so you can download a fixed driver or malware tool.

Safe Mode with Command Prompt — boots to cmd.exe instead of the desktop for scripted repair.

Access it from Settings → System → Recovery → Advanced startup , or WinRE → Troubleshoot → Advanced options → Startup Settings → Restart , then press 4 / 5 / 6 (or F4/F5/F6). msconfig (System Configuration → Boot tab) can also force the next boot into Safe Mode — remember to uncheck it afterward or the PC keeps booting safe.

Slow-Performance Triage

Open Task Manager (Ctrl+Shift+Esc) and sort by CPU, Memory, and Disk to find the resource hog.

Disable unneeded startup programs (Task Manager → Startup apps).

Scan for malware — a hidden miner or adware is a classic cause.

Confirm at least 15–20% free space on the system drive; a near-full SSD throttles hard.

Check drive health via SMART (chkdsk, or a SMART utility) — rising reallocated-sector counts mean a failing disk.

Common Windows Issues

  • Issue Causes Fix
  • Frequent freezes Bad RAM, driver, overheating Test RAM, update drivers, check temps
  • "Connected, no internet" DNS, proxy, IP conflict ipconfig /flushdns , release/renew, check proxy
  • Profile won't load Corrupt user profile Create new profile, migrate data
  • Wrong time/date Dead CMOS battery, NTP off Replace battery, enable time sync
  • System Restore

System Restore rolls back system files, the registry, drivers, and installed programs to a saved restore point (launch with rstrui.exe ). It is ideal after a bad update or driver. It does not touch personal documents, photos, or music, and it is not a backup — for user data you need File History or a real backup. Because malware can survive a restore, always run an antimalware scan after restoring.

Exam logistics: The current A+ Core 2 is 220-1202 (V15) — up to 90 questions in 90 minutes , passing score 700 of 900 , including drag-and-drop and performance-based items. The retired 220-1102 listed this domain at 22%; V15 raises it to 23% .