Power Supply problem?

OK - got a system that's been absolutely rock solid for a good year - now it won't boot - I press the on button, fans spin, and then nothing - no beep codes, just whir of fans.

Tried removing all the various bits - still won't boot without any hard disks and with either stick of RAM taken out or with no graphics card, I've checked all the power connections / removed all unnecessaries and the bugger still won't give me that nice "all ok" beep.

I'm not barking up the wrong tree when I guess that it's probably the PSU no longer being able to supply the necessary juice, is it? I mean, it could be the motherboard, but that's really the less likely option here, right?

If so - suggestions for a new unit\would be excellent please - it's potentially got to power a decent athlon 64 system with a x800gto2...

the only way to find out is try another one but.... it sound like the mobo beacuse it dont take much power to boot in dos or on the post screen as said b4 try another psu

could be a borked BIOS