I apololgise if this has already been answered, but I had a look for the same problem and couldn't find anything.
Recently my power supply went bang, so having replaced it (with a slightly more powerfull one) it worked ok for a week. Just tried to boot it up (having not touched anything since it closed down working fine) and nothing happens. The PSU fan is spinning, the CPU fan is spinning, the LED on the motherboard is lit and my keyboard CAPS etc is lit. Apart from that nothing. Monitor is telling me its getting no signal, hard drives aren't spinning, CD drives won't open.
Have tried checking all the connections, gone right back to the basic system (just monior and keyboard, with no hard drives, USB et.) and not even the BIOS will come up. I have cleared the CMOS and removed and replaced the graphics card and RAM, so have run out of ideas.
I havn't got any spare parts around so can't really test anything, and didn't wanna have to buy new parts unless it's absolutely necessary.
Any ideas would be awsome?