I have a Windows 7 Ultimate computer (Shuttle) that I built myself and in it I put a Solid State Drive (SSD). It's been working well for a number of months but now when I start it there are problems.

I have 2 users setup on the computer and when I try and sign in with either user it claims that the password is incorrect. I could understand the odd typo but I've had my wife try it as well and we've got the passwords correct.

On top of that it will remain at the login screen for 1 minute and 20 seconds and then spontaneously reboot without shutting down.

So I'm trying to work out if this is a hard disk problem or something else. Any ideas?

(I have a nightly backup to a WHS so it will be easy to recover but I don't want to do that unless I have to and don't want to waste time putting in a new HD just to discover it's something else.)

More info: If I start in Safe Mode I am able to login with the password and all appears as normal as it can in Safe Mode. However, normal boot continues with same problem.