Complete Computer Troubleshooting Cheatsheet: Diagnose & Fix Common Problems

Introduction to Computer Troubleshooting

Computer troubleshooting is the systematic process of identifying, diagnosing, and resolving hardware, software, and network issues. Effective troubleshooting combines technical knowledge with a methodical approach to isolate problems and implement appropriate solutions, saving time and preventing data loss.

Core Troubleshooting Methodology

The Universal Troubleshooting Process

1. Identify symptoms: Document exactly what’s happening
2. Isolate the problem: Determine if it’s hardware, software, or network-related
3. Reproduce the issue: Can you make it happen consistently?
4. Simplify the system: Remove variables by disconnecting peripherals or closing applications
5. Try simple fixes first: Restart, update, check connections
6. Research similar issues: Search for error codes or specific symptoms
7. Test potential solutions: Apply one fix at a time
8. Verify resolution: Confirm the problem is fixed and won’t recur
9. Document the solution: Record what worked for future reference

Essential Diagnostic Tools

• Built-in diagnostics: BIOS/UEFI tools, Windows Memory Diagnostic, SMART disk checks
• System information tools: Device Manager, System Information, Task Manager
• Third-party utilities: Hardware monitors, diagnostic software
• Rescue media: Bootable USB drives with repair tools

Quick-Reference Troubleshooting Flowchart

START → Computer won't power on → Check power connections → Check power supply → Hardware issue
      ↓
Computer powers on but won't boot → Check boot device → Check for BIOS/UEFI errors → OS repair
      ↓
Computer boots but runs poorly → Check resource usage → Scan for malware → Check startup items → Software issue
      ↓
Specific application not working → Update application → Reinstall application → Check compatibility
      ↓
Internet connection issues → Check local connection → Check network devices → Contact ISP

Hardware Troubleshooting

Computer Won’t Power On

POST Beep Codes and LED Diagnostics

• 1 beep: Normal boot
• 2 beeps: CMOS/BIOS configuration issue
• 3 beeps: Memory issue
• Continuous beeps: Power supply or motherboard issue
• LED error codes: Consult motherboard manual for specific patterns

Display Problems

• No display output:

  1. Check monitor power and connections
  2. Try different video cable/port
  3. Test with different monitor
  4. Reseat graphics card (if applicable)
  5. Test integrated graphics (if available)

• Distorted display:

  1. Update graphics drivers
  2. Check cable connections
  3. Reset monitor settings to default
  4. Test different resolution settings
  5. Check for overheating GPU

Storage Device Issues

• Hard Drive/SSD not detected:

  1. Check data and power cables
  2. Test in different SATA port
  3. Check drive visibility in BIOS/UEFI
  4. Try drive in different computer
  5. Check for clicking sounds (HDD failure)

• Drive detected but shows errors:

  1. Run CHKDSK (Windows) or First Aid (Mac)
  2. View SMART data for health status
  3. Test with disk diagnostic utilities
  4. Backup data immediately if possible
  5. Consider drive replacement if SMART fails

Peripheral Connectivity Issues

• USB devices not working:

  1. Try different USB port
  2. Restart computer with device connected
  3. Uninstall and reinstall device drivers
  4. Check Device Manager for errors
  5. Test device on different computer

• Bluetooth problems:

  1. Verify Bluetooth is enabled
  2. Restart Bluetooth service
  3. Remove device and re-pair
  4. Update Bluetooth drivers
  5. Check for device compatibility

Software Troubleshooting

Operating System Won’t Boot

Windows Recovery Options

• Safe Mode: Windows key + R → msconfig → Boot → Safe boot
• Startup Repair: Boot from Windows installation media → Repair options
• System Restore: Start → type “recovery” → Open Recovery → System Restore
• Reset PC: Settings → Update & Security → Recovery → Reset this PC

macOS Recovery Options

• Safe Mode: Hold Shift during startup
• Recovery Mode: Command + R during startup
• Disk Utility: Boot to Recovery Mode → Disk Utility
• Reinstall macOS: Boot to Recovery Mode → Reinstall macOS

System Performance Issues

• Computer running slowly:

  1. Check Task Manager/Activity Monitor for resource usage
  2. Scan for malware/viruses
  3. Disable unnecessary startup programs
  4. Clear temporary files
  5. Defragment HDD (not for SSDs)
  6. Consider hardware upgrades (RAM, SSD)

• Application freezes or crashes:

  1. Force quit unresponsive application
  2. Update application to latest version
  3. Check for OS compatibility
  4. Reinstall application
  5. Check error logs

Critical Windows Troubleshooting Commands

sfc /scannow                 # System File Checker - repairs Windows files
DISM /Online /Cleanup-Image /RestoreHealth  # Repairs Windows image
chkdsk C: /f /r              # Check disk for errors and bad sectors
powercfg -energy             # Power efficiency diagnostics
netsh winsock reset          # Reset Winsock catalog
ipconfig /flushdns           # Clear DNS cache

Critical macOS Troubleshooting Commands

diskutil verifyVolume /      # Verify disk structure
diskutil repairVolume /      # Repair disk issues
sudo periodic daily weekly monthly  # Run maintenance scripts
sudo nvram -c                # Clear NVRAM
sudo dscacheutil -flushcache # Flush DNS cache

Network Troubleshooting

Internet Connection Issues

Network Diagnostics Commands

Windows:

ipconfig /all                # View all network configuration
ping google.com              # Test connection to external server
tracert google.com           # Trace route to destination
netstat -a                   # View all active connections
nslookup google.com          # DNS lookup

macOS/Linux:

ifconfig                     # View network configuration
ping google.com              # Test connection
traceroute google.com        # Trace route to destination
netstat -a                   # View all active connections
dig google.com               # DNS lookup

Wi-Fi Troubleshooting

• Cannot connect to Wi-Fi:

  1. Toggle Wi-Fi off and on
  2. Forget network and reconnect
  3. Reset network settings
  4. Update network adapter drivers
  5. Check for MAC address filtering

• Weak Wi-Fi signal:

  1. Move closer to router
  2. Remove physical obstructions
  3. Change router channel
  4. Update router firmware
  5. Consider Wi-Fi extender

Common Error Messages and Solutions

Security Troubleshooting

Malware Symptoms and Removal

• Common malware symptoms:

  • Unexpected pop-ups and redirects
  • System slowing significantly
  • Unusual network activity
  • Files encrypted or missing
  • Disabled security software

• Malware removal steps:

  1. Boot into Safe Mode
  2. Update and run antivirus/anti-malware scans
  3. Use multiple scanning tools
  4. Remove suspicious programs
  5. Reset browsers
  6. Change sensitive passwords after cleanup

Account and Password Issues

• Cannot login to user account:
  1. Verify Caps Lock is off
  2. Try password reset options
  3. Use alternative admin account
  4. Check for account lockout policies
  5. Use system recovery options

Preventative Maintenance

Regular Maintenance Schedule

Backup Best Practices

• 3-2-1 Backup Rule:

  • 3 copies of data
  • 2 different storage types
  • 1 copy off-site or cloud-based

• Critical items to backup:

  • Documents and work files
  • Email archives
  • Photos and videos
  • Browser bookmarks
  • Application settings

Advanced Troubleshooting Techniques

Boot Repair and Recovery

• Repair Windows boot records:

  bootrec /fixmbr
  bootrec /fixboot
  bootrec /rebuildbcd
  

• Repair GRUB (Linux):

  sudo grub-install /dev/sdX
  sudo update-grub
  

Data Recovery Options

• Software-based recovery:

  1. Try built-in tools (Previous Versions, Time Machine)
  2. Use data recovery software (Recuva, TestDisk)
  3. Don’t install recovery software on the problem drive

• Professional recovery options:

  1. For critical data or physical drive damage
  2. Cleanroom recovery services
  3. Can be expensive but higher success rate

Resources for Further Help

Reliable Troubleshooting Websites

• Microsoft Support: support.microsoft.com
• Apple Support: support.apple.com
• Stack Exchange: superuser.com
• Bleeping Computer: bleepingcomputer.com
• Tom’s Hardware: tomshardware.com

Diagnostic Tools

• CrystalDiskInfo (drive health)
• MemTest86 (RAM testing)
• HWiNFO (system information)
• Wireshark (network analysis)
• Process Explorer (advanced Task Manager)

When to Seek Professional Help

• Physical damage to components
• Electrical issues or burning smells
• Drive making clicking/grinding noises
• Critical data recovery needs
• Persistent issues after exhausting DIY options

This cheatsheet provides a structured approach to identifying and resolving common computer problems. Remember that patient, methodical troubleshooting is often more effective than random fixes, and always backup important data before making major system changes.