I have a Dell Dimension 8400 desktop, and am running XP Home edition. When I turn on my computer, the power supply fan and the processor fan run unusually loud. The computer doesn't start up at all. The diagnostic lights on the back panel don't light up. Nothing works except the fans My wife discovered the problem yesterday when she turned on the computer. I tried unplugging the power cord on both ends and replugging the ends back in. It doesn't even get to the BIOS.
I would appreciate any help with this issue.

It's a bit difficult to diagnose a problem like this without having access to at least the BIOS.

Have you had any power surges/lightning storms recently? Have you done anything to the computer recently (added hardware or software - or changed or removed any)?

If the processor fan is running, there's probably power to the motherboard - so I wouldn't suspect the PSU as a likely suspect.

*plays taps for the motherboard* A computer that was just restarted that can't even get to post? hm... Well, let's troubleshoot it anyhow.

First off, are you sure your monitor is working? It's plugged in and everything? Whenever you turn the computer on, do hear the sound of the hard drive working or the one beep of the system clear? Wait about five minutes, and if you don't hear anything different... well you could open the computer and check on the fans, but it sounds like a fry to me...