In some cases, malware prevents you in opening MSCONFIG; you can download Emergency Utilities to create usable copies of MSCONFIG, Regedit, and Task Manager from Doug Knox’s website. Use the MSCONFIG from that download to set up the PC to boot into Safe Mode. If this utility will not help to boot the computer in Safe Mode, malware like the Conficker worm might have deleted the registry key in Windows that will allow the computer to boot to Safe Mode. If that is the case, you should get rid of the malware by using an antivirus rescue CD e.g. AntiVir Rescue System, Sunbelt’s VIPRE Rescue, Panda SafeCD, etc.
Once the computer is malware-free, you can proceed to boot to Safe Mode to troubleshoot Windows but I suggest running the System File Checker Utility in Windows to replace or fix any damaged or deleted system files that a malware or buggy software and driver have caused on the system: Click on Start → Run → type cmd → press Enter key on the keyboard.
Note: Vista and Windows 7 users need to run the command prompt as admin. Click Start → All Programs → Accessories → right-click Command Prompt and select "Run as Administrator." Then type cmd and press Enter.
In the Command prompt window, type SFC /scannow then press the enter key on the keyboard to allow SFC utility to scan the computer for any damaged or corrupted system files. If that helps and you've finished using Windows in Safe Mode, proceed to run the Windows Update program in Vista or Windows 7 or visit the Windows Update website to ensure that the replaced system files by SFC utility is patched.
