Computer turns on but display nothing

My mobo is Abit at8 32x with 3 GB of ram, geforce 8800 gts, 500 watt psu and athlon FX-60. Today the unit turns on but display nothing, i've reseated the ram but it not working and i've test the video card on a different computer and it work fine. When I reset the bios with the jumper, it able to display the post screen but when you reset the computer, it doesn't display anything until you do another bios reset. I've also switch out with the spare PSU and it still doing the same thing.

I noticed that the mobo only only display 1.5 GB of ram when I've 3 GB installed and when I removed 2 GB out of the mobo, reset the bios and boot up, it only detect 1.5 GB.

When it doesn't display anything the mobo give 9.0 code and when I completely remove all the ram, it display a C1 code.

I've spent 5 hour doing diagnostic and found nothing. Please help.