Windows OS Troubleshooting
Key Takeaways
- Blue Screen of Death (BSOD) indicates a critical kernel-level error — common causes include bad drivers, failing RAM, corrupted system files, and overheating; check the stop code for specific diagnosis.
- Safe Mode loads Windows with minimal drivers and services — use it to uninstall problematic drivers, remove malware, and troubleshoot startup issues that prevent normal boot.
- System Restore returns system files and settings to a previous point in time WITHOUT affecting personal files — it does NOT work as a backup for user data.
- Windows Recovery Environment (WinRE) provides Startup Repair, System Restore, Command Prompt, System Image Recovery, and Reset this PC when Windows cannot boot normally.
- Slow performance troubleshooting: check Task Manager for resource hogs, disable unnecessary startup programs, scan for malware, check disk health, verify sufficient free disk space (at least 15-20%).
Last updated: March 2026
Windows OS Troubleshooting
Blue Screen of Death (BSOD)
A BSOD occurs when Windows encounters a critical kernel-level error that it cannot recover from. The system stops to prevent data corruption.
Common BSOD Stop Codes
| Stop Code | Likely Cause | Solution |
|---|---|---|
| IRQL_NOT_LESS_OR_EQUAL | Bad driver, faulty RAM | Update/rollback drivers, test RAM |
| PAGE_FAULT_IN_NONPAGED_AREA | Faulty RAM, corrupt drivers | Test RAM with Memory Diagnostic, update drivers |
| SYSTEM_SERVICE_EXCEPTION | Incompatible driver, corrupt system file | sfc /scannow, update drivers |
| CRITICAL_PROCESS_DIED | Corrupt system files, malware | sfc /scannow, DISM, scan for malware |
| DPC_WATCHDOG_VIOLATION | Driver timeout (often SSD/storage driver) | Update storage controller driver, firmware |
| KERNEL_SECURITY_CHECK_FAILURE | RAM issue, corrupt file, driver problem | Test RAM, run sfc, update drivers |
| DRIVER_IRQL_NOT_LESS_OR_EQUAL | Specific driver failure (name often shown) | Update or remove the named driver |
| UNMOUNTABLE_BOOT_VOLUME | Corrupt boot sector, failing drive | Boot from recovery, run chkdsk /f /r |
| INACCESSIBLE_BOOT_DEVICE | Changed SATA mode, missing driver | Check BIOS SATA settings, install storage driver |
BSOD Troubleshooting Steps
- Note the stop code and any driver file mentioned
- Restart and see if it happens again — a single occurrence may be a one-time glitch
- If it repeats, boot to Safe Mode and:
- Roll back or update the most recently changed driver
- Run sfc /scannow and DISM /RestoreHealth
- Test RAM with Windows Memory Diagnostic
- Check Event Viewer for related errors
- If it started after a driver or Windows update, use System Restore to roll back
Boot and Startup Issues
Windows Boot Sequence
- POST — Hardware self-test
- UEFI/BIOS — Finds boot device
- Boot Loader — Windows Boot Manager (bootmgr) loads
- Windows Kernel — ntoskrnl.exe loads, drivers initialize
- Session Manager — smss.exe starts core processes
- Login Screen — winlogon.exe presents the login prompt
Common Boot Problems
| Problem | Symptoms | Solution |
|---|---|---|
| Bootmgr is missing | Error message before Windows loads | Repair boot sector from WinRE, run bootrec commands |
| Spinning dots, never loads | Windows logo but never reaches desktop | Boot to Safe Mode, check for driver issues |
| Boot loop | Keeps restarting before reaching login | WinRE → Startup Repair, or System Restore |
| Black screen after login | Login works but desktop never appears | Ctrl+Alt+Del → Task Manager → run explorer.exe |
| Constant automatic repair | WinRE loops without fixing | Use Command Prompt in WinRE to run sfc, DISM, chkdsk |
Boot Recovery Commands (from WinRE Command Prompt)
| Command | Purpose |
|---|---|
bootrec /fixmbr | Writes a new MBR to the system partition |
bootrec /fixboot | Writes a new boot sector |
bootrec /rebuildbcd | Rebuilds the Boot Configuration Data |
sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows | Offline system file check |
chkdsk C: /f /r | Check and repair disk errors |
Safe Mode
Safe Mode loads Windows with minimal drivers and services for troubleshooting:
| Safe Mode Type | Description |
|---|---|
| Safe Mode | Minimal drivers, no network, basic display |
| Safe Mode with Networking | Same as Safe Mode but with network drivers (for downloading fixes) |
| Safe Mode with Command Prompt | Minimal drivers, boots to CMD instead of desktop |
How to Access Safe Mode:
- From Windows: Settings > Recovery > Restart Now → Troubleshoot → Advanced Options → Startup Settings → Restart → F4/F5/F6
- From Boot: Hold Shift while clicking Restart, or interrupt boot 3 times to trigger WinRE
- From WinRE: Troubleshoot → Advanced Options → Startup Settings
Common Windows OS Issues
| Issue | Possible Causes | Solutions |
|---|---|---|
| Slow performance | Too many startup programs, malware, full disk, failing drive | Disable startup programs, scan for malware, free space, check SMART |
| Frequent freezes | Bad RAM, driver issues, overheating | Test RAM, update drivers, check temps |
| Application won't install | Insufficient permissions, incompatible, corrupt installer | Run as Admin, check compatibility mode, re-download |
| Application crashes on startup | Corrupt settings, missing dependency, compatibility issue | Reinstall, clear app data, compatibility mode |
| No internet but connected | DNS issue, proxy misconfigured, IP conflict | Flush DNS, check proxy, release/renew IP |
| Profiles not loading | Corrupt user profile, registry issue | Create new user profile, copy data |
| Time/date wrong | Dead CMOS battery, wrong time zone, sync disabled | Replace battery, set time zone, enable NTP sync |
| USB device not recognized | Driver issue, bad port, power insufficient | Try different port, update driver, use powered hub |
System Restore
- Reverts system files, installed programs, registry, and drivers to a previous point in time
- Does NOT affect personal files (documents, photos, music)
- Does NOT serve as a backup solution
- Restore points created automatically before updates and installs, or manually
- Access: Control Panel → Recovery → Open System Restore, or
rstrui.exe
Warning: System Restore may not undo malware infections. Run antimalware AFTER restoring to ensure the system is clean.
Test Your Knowledge
A Windows computer shows a BSOD with the stop code IRQL_NOT_LESS_OR_EQUAL. What are the two MOST likely causes?
A
B
C
D
Test Your Knowledge
What does Safe Mode do in Windows?
A
B
C
D
Test Your Knowledge
System Restore is used to:
A
B
C
D
Test Your Knowledge
A Windows computer is stuck in a boot loop and cannot reach the desktop. What recovery tool should you try FIRST?
A
B
C
D