Last night my XP2400 decided to power down and doesnt want to come back on!

To make it do anything I have to unplug the power supply, plug it back in and switch on, it then attempts to boot for anything between .5 second to 5 seconds. Lights flash and I have seen the cpu fan and the internal PSU fan rotate and once I actually got a beep! I have not seen the external PSU fan move at all (but perhaps this starts up later in the boot sequence?).The power then switches off.

I have tried a barebones boot and the response from the system is identical. The more often I have tried to boot it the less time it seems to have power.

My hope is that the PSU is cutting out for some reason but I fear something worse! Anyone seen this behaviour before?

/edit Seems to be getting worse, all I get now is a quarter turn of the cpu fan?

TIA

Update:

I have removed the PSU and tested it with a wire between the on pin and a ground pin and only the internal fan is operating. Is it likely then that either my motherboard or CPU got cooked? If so is there any way that I can tell which?

If you are hearing the beep after the post I would say your motherboard is working. Checking the power suply and replacing it is the first thing I would do cause the fan (PSU fan) should start working once it is on.

Thanks, I thought that single beep might be good news! New PSU arrives today so fingers crossed.