I have an 8 year old Dell Desktop, 2ghz, 2gb, 500gb HD with 500gb secondary drive. Never had problems with it until now. There have been no software/hardware changes in 6 months. Starting yesterday after it had been on for about four hours I went to use it and it was frozen. I rebooted and it worked fine. This scenario repeated itself three more times yesterday. Today it happened again after being 6hours. When I rebooted it today it couldn't find the hard drive. I tried to reboot several times and got the same cannot find the hard drive press F2 for setup. I shut it off and let it set for three hours. When I turned it on everything worked fine. Currently creating a fresh backup.
Obviously something is failing, but what? This 'puter has been flawless from day one.
Sounds like it could be a hard drive failure to me, at least thats the first thing that comes to mind. Another possibility is a motherboard problem. I would make sure you get a good backup, and then try removing the drive that you've been using and try reinstalling windows on the secondary drive and see what happens. if it happens again, it isn't the HD, but if it solves your issue, its the drive failing. I have had drives fail that way.
Agree with the failing hard drive diagnosis. Almost every drive I've had that's failed worked intermittently for a while before biting the dust. That seems to be the norm now instead of the clicks of death they used to do.