When you say you have tried a repair, have you tried running chkdsk or copying the corrupted part of the registry (\config\system)?
If not, try these:
1. Boot to the Recovery Console and at the prompt, type chkdsk /r and press Enter.
2. If chkdsk doesn’t clear it up, try copying the previous \config\system file. There is a full explanation here
http://support.microsoft.com/?kbid=307545 Note the guided help download will not help you as you can’t boot to Windows.