No display or beeps. Tried everything and out of ideas.

Hi all,

This is my first post   and I hope ive posted it in the right place.

Well a few days ago I bought a new Antec 300 case and a heatsink for my computer
Installed everythin today, I had to snap off the legs to make the heatsink fit but apart from that all went well.
I turned my computer on and No display, no beeps and no lights on the keybaord but all fans and hard drives were working.

Heres my spec:
AS-Rock k8 combo z (I know its old!)
AMD-Athlon 64
800 watt PSU
2gb Crucial RAM
Radeon AGP 8x 3850 Gfx Card - No onboard video

Well ive been up all night troubleshooting and this is what ive done so far.

1) Taken motherboard out of computer and stripped computer to PSU, Gfx card, 1 stick of RAM and keyboard to isolate the problem. I used a anti static matt.
2) Monitor works fine when connected to another computer
3) Tried running my computer on another monitor but no display or beeps
4) Installed my old heatsink again and same problems
5) Ive tried another PSU, Gfx card and RAM (All working on my mates computer) on my motherbaord but the same problem
6) Ive tried my PSU, Gfx card and RAM in his computer and they work fine.
7) Booted with no RAM and I get error beeps but no display
8) Resetting CMOS using the jumper method and removing battery but same problem
9) Checked the processor by removing heatsink and turning computer for a few seconds. Processor heats up so thats a good sign

And even after all that it hasnt made a single difference!
It cant be the Gfx card, RAM or PSU.
Not sure about motherboard or Processor

Im totally lost for solutions, I hope someone can help. It seems to me its that I could have damaged the motherboardsomehow in the process but not too sure. Im going crazy

Thanks in advance