No Beep, CPU failed?

Hello!
I have a problem here. My computer doesn't startup anymore. The fans will start rotating and everything but there won't be the typical BIOS Beep when it starts booting up. The screen stays blank and there won't be any indication of booting. It just stays like this, with the fans all working but except that, nothing.
So I was reading around the internet what could be the causes of such behavior...
I read horror stories, that it's the CPU which is broken. Or the Motherboard.
A little bit history:
Since one time I was getting regular BSOD's. They appeared after I hard reset when my PC froze while playing Battlefield 2142. It all went downhill from now on.
The 2 free PCI Slots of my motherboard were not usable anymore. When I put in my Soundcard, it would freeze WHILE booting into Windows. And it could not be the Soundcard since I bought a new one and the same thing happened.
So I was using the On-Board sound. And it worked for some time.
Until I was getting frequent BSOD's even when I didn't do anything with the computer. It could happen while browsing or listening to music. This just happened a few days ago.
So yesterday I once again had to hard reset my computer... When trying to boot up again, it would tell me that there is corrupted file in Windows/System32/ and I should repair it before I can boot again.
So I took the IDE Harddisk from my brother which was flattened some time ago. (My actual harddisk was a SATA)
And I tried booting. But now, it would start with having no beep anymore, Screen staying blank etc...
My Specs:

Gigabyte K8 NF9 Motherboard
AMD Athlon 64 X2 4400+
Geforce 7800 GT 512MB
2X 512MB Vdata 3200 RAM
160GB Maxtor Harddisk SATA

I would guess its the motherboard... Because of the issue with the two soundcards before. But I can not be sure of that. Maybe someone here can guess a little better than me. :-) Thanks everyone.