black screen help!!!

alright so my problem is when i boot up my computer it shows the black screen of death! I did a bunch of different things and nothing seems to work. I tried a different monitor, a different brand new video card, checked the jumpers, cleared the cmos, removed all pci cards and put them back, nothing works. when i boot up the computer it doesn't make a beeping noise like it used to and the keyboard and mouse do not light up at all.

computer specs

Intel 2.8c hyper threading
asus p4c800 dlx
ocz 1 gig dual channel premier series
bba ati radeon x800 xl
western digital 160gb sata
creative sound blaster audigy 2 zs
thermaltake 480 watt psu

Video graphics card gone bad, or something has become unplugged, such as a cable, or bent such as a graphics cable socket or plug.

how can the video card be the problem?
i also thought the video card was the problem so i rmad it and ati just sent me another x800l looks brand new to me
i installed it yesterday and iam sitll having the same problem