The fan might be running on mains voltage, try swapping the PSU.

Your PSU has died, you might be able to get it 1/2 way running again by unplugging all un-needed devices (cdrom 2nd HD etc) but its time for a new PSU

It's impossible to say with certainty, but I would be more inclined to guess that the motherboard/CPU has failed (esp if the CPU fan spins, but you may be hearing the PSU fan).

If LEDs light up on the keyboard, even for a moment when switching on, this usually means the power supply is ok. The only way to be certain is to swap components.

Kaled.

when a CPU fails the the whole computer fires up and runs - PSU, fans, disks....except it never does anything beyond that. You'll be looking at a blank screen
a MB would have to be pretty burnt up to not even relay a power on to the PSU.

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take the PSU to another computer real fast and if it does the same thing in that machine throw it in the trash.

[edited by: J_RaD at 1:59 pm (utc) on May 27, 2009]

take the PSU to another computer real fast and if it does the same thing in that machine throw it in the trash

DO NOT plug a suspect PSU into a working machine, you could damage your other PC.

If you cannot check the output voltages from the PSU, swap it out with a working one and see what happens.

In our throwaway disposable culture just yank the drive from that critter and install on a recession priced critter and get back to work. Some of these things don't need to be solved these days. Just get back to work.