Hello, this problem started yesterday when i came home and realized that my computer had freezed, i pushed the reset-button and everything booted up normally...

After running a couple of hours the computer froze again, the mouse was stuck and it didn't respond to keyboard.. so i pushed reset again and everything booted up normally..
Then again after running about 1 hour it froze again, the same way as before.. only this time when i pushed reset, i got something like

crc error - System halted

Or something like that (i don't remember the exact message..)
Anyway after this when i powerd it down, it doesn't start anymore.. i can hear the harddrives/cdrom/cpufan start but i don't get any picture on the screen..

Anyone have any ideas about what this could be? Harddrive crash?

CRC error is usualy hdd or chipset trouble... Maybe you hdd is dying (or already dead?) or your chipset fried, it's really hard to tell.
The "blank" screen may be caused by some severe failure (chipset, motherboard?) or if you are lucky something less important. Try to unplug everything not needed, especially the RAM if you have spare modules and the HDD , then try to boot. The idea is to find out what hardware is failing. It could be anything, usually it's the part you don't think of (ever heard of murphy law?), so don't be hesitate to unplug even hardware you don't think that could be related (network card, video card, modem...). But my guess is that the trouble is about the RAM or the Chipset, RAM might have been damaged by power shortcut/overtension and chipset by heat.

In any case, I wouldn't try to boot from the hdd now, get a livecd (knoppix as example), then boot from it (make sure it doesn't mount the hdd automatically). Then, I would suggest to disable DMA, as it is very intensive for the hdd, and to backup all you can before you can't no longer...

I have tried unplugging hdds + cdrom, memory, soundcard... it still doesn't work

The power supply maybe? I saw one time a broken PSU, that wasn't providing enought power, randomly freezing a computer everytime at boot... I don't have much hope but it might worth to try. :/

I Think i have found an answer
I have been cooling my cpu with watercooling + peltier for the past 2 weeks... (before that i had just the watercooling) and it seems like the isolation (?) has been poor, the top of the cpu was all wet from condens water!

The mainboard is completley dry i think.. at least i don't see any water.. Could this be the reason for the crc error?

Well... computer hardwares and water aren't friends, if some important part got wet, it is very likely there have been some short-circuit somewhere... I never heard about electrical problem on a CPU, but I suppose it is possible.

CRC is some kind of verification calculation I believe, CRC error would mean the verification algorithm returned an error. So I guess it could almost anything, including a dying CPU, even if I my first guess would be something bad about the motherboard

I'll let the components dry a while now before i'll begin testing them..
I think i'll have to go and buy a cheap cpu- and nbcooler so i don't have to fight around with the watercoolingsystem any more.. it was fun while it lasted, but it feels like it takes up too much time...

tell us if the computer come back to life then

Yep I'll have to wait until tomorrow i guess.. no stores open at this time I can almost say that i hope i'ts the cpu.. because it's a pretty cheap AMD Duron 1800.. But i'll report back to you guys after i'm done testing..

Ok.. now i have installed heatsinks and fans on CPU, NB, and GPU.. and it powered up on the first try ... maybe it was just the water on the cpu? Anyway i'm kinda happy

uuuuh... Maybe, but if so, you are really the most lucky geek ever
Usually water on electronic device tend to kill every circuits, not to temporary make them unable to work... Make sure to give a sacrifice to the god of geek

Hehe yep i feel kinda lycky I really can't see any other reason for the hangup.. I just let the parts dry for about 2 days while I waited for the heatsinks that i ordered to arrive (so it would be simpler to switch the processor with my server when testing), but I didn't have to I didn't change anything in any way except for letting the parts dry.. kinda strange.

But anyway thanks a lot guys