I encountered a Windows 7 computer that would only boot to a black screen. The only thing I saw was a mouse arrow. At first I suspected the hard drive was corrupt, so I cloned the hard drive. But the problem still existed. With this computer I still had reason to believe the hard drive was bad. Next I scanned for a virus in Windows directory and the only that was discovered was one of those junk free programs that deliver pop-up ads.
It was at this point that I decided to try an easy solution. Since this was Windows 7 there would a good copy of the registry files at %windir%\system32\config\RegBack\. So after making a backup of the current registry files, I copied the good registry over the current ones. With this computer, some of the current registry files were twice as big as the good copies, which is why I think something was wrong with the old hard drive. After I did this, the computer booted fine.
Some other suggestions included running System Restore. I was lazy in this instance and didn’t try that. But I did increase the System Restore capacity once I got back into Windows. If you are still using Windows XP, you can always find the registry files under the \System Volume Information\ folder. Some other suggestions are that certain key folders have been corrupted or have corrupt permissions. Check the Windows folder, the Program Files folders, and the Recycle Bin folder.