New Win7 install, hangs at startup screen (black)

Hi,

After a fresh install, basic programs, Office etc, the computer has been running great. A few days later, after being rebooted, it has decided to hang at the login screen.

It will show the cursor, play the 'welcome to windows' sound, but not actually show the user accounts and allow logging in. After maybe 15 minutes, the login screen will appear, and you can log in as someone, but it will again just hang at a black screen indefinitely.

Loading with "Last known good configuration" doesn't help. Loading in safe mode allows it to work fine but I can't track down why this is occurring.

I don't want to format again when I don't even know what went wrong. Suggestions?

EDIT: I uninstalled Nvidia drivers in Safe mode and now when I boot normally, I see the blue Windows 7 Ultimate login screen background but none of the user accounts on the machine. The tower just sits there like an idiot with the hard drive light flashing briefly in 1 second intervals.