I'm a developer, but it appears I've royally screwed my machine.
I was debugging my code with WinDbg (novice user) trying to figure out an issue and I ran gflags.exe and enabled the checkbox for Application Verifier. I restarted WinDbg and Windows complained it couldn't start the application. I thought it was some weirdness with WinDbg, but then I noticed I couldn't run my web browser with the same error message. My machine eventually locked up on me so I said screw it, and I rebooted my machine.
Now when I start the machine it says Windows can't start, if I don't run the repair program it just hangs with a blinking underscore. I ran the repair program which says it will try to restore it, but this was at the end of the day on my work machine so I had to head home.
I can understand how enabling Application Verifier could screw up an application, but how in the world did it bring my whole system down?
Windows 7 64-bit.