Try carefully removing the expansion cards, memory and then replace them. Also check for blocked fans on the CPU, GFX card case fans as these can overheat your system and cause damage.
If you can identify your motherboard you should be able to get onto their website and find out what the beeps represent.
JUST.. in case.. Reset your bios. There is two little metal prongs sticking near each other somewhere on the motherboard, usually near the battery. If you got a PATA hdd, or CDrom, you can see there is a little bracket on the backside. This fits the prongs for resetting bios. If youdont feel comfortable with that, or your mobo does not have it.. which can.. happen.. just pull the battery out and wait a minute and put it back in. See if that works. Not likely, but it is the fastest most hopeful quick solution you got.
Unhook your HDD
Take out your Graphics card
Take out all of your PCI cards, I.E. sound card.
Take all but one stick of ram.
Turn it on. See if it turns on and stays on. Should hear a single beep. If so, great. If not, then you can either yank out the stick of ram and instead put the other stick in. Repeat. If it works, great. If it does not, then...your CPU is fried if your fans/lights on the mobo turn on, which with beeping they do.
Your culprit is one of three things.
You hearing beeps, seeing fans/lights, etc, means your chipset is fine. If you put in one stick of ram and it works but not with both, one of your sticks fried. If it works till your GPU, then that is fried..
Even on a fried GPU you still get past post. Trust me, I have hehe. So i am leaning heavily towards CPU or Ram. If it was the GPU also, you would get either <No signal at post or <alot of tiny flashing dots. Your black screen comment might be the no signal? Or does the monitor turn on from a dead start? If it turns on, like clicks, the GPU is still sending the signal to turn on.
So.. I am gonna say if the bios reset does not work.. pray it is the ram. If the ram isnt it, then your CPU is borked. Your motherboard is fine. It wouldnt tell you "Hey.. something is wrong here!" if it was fried. Dont listen to someone telling you it might be the mobo.
Post for me more information.. try what i said. Might be a simple and easy fix. But no promises.
I want to discredit sto from killing his computer as well but I just got done downloading the patches about 30 minutes ago and my computer just shut off on me as well. It wouldn't come back on either for about 10 minutes. I can't figure out why. I finally got it back on. It's running at 30.3 degrees Celsius according to my thermometer, so it's not overheating. And I built it myself, with quality parts. I can't figure out what might be causing it.