No Display after Windows XP Update/Restart

I just replaced the ram in my computer, and after some dual-channel issues with that I finally got everything running great. Computer would POST successfully, shutdown/restart all good. But today, after a Windows XP update, I was asked to restart my computer so I did. Then when my computer did the restart, nothing. I dont know how to find out what this problem is. When I turn on my computer, everything turns on (HDD, GPU, Mobo lights up, LEDs light up, fans, everything, even the keyboards, external hard drive, usb hub and even my effin iPhone lights up when I plug it into the dock!) But I get no display on the monitor at all. Funny thing is, the monitor doesnt say "No Signal" when I turn my computer on the monitor lights up indicating that its getting a signal from the GPU. But I get nothing on the display, no BIOS screen, no Windows XP boot screen, NOTHING. Its driving me nuts. Its as if the computer is booting properly just without any display. At first I thought maybe my RAM was acting up again, so I took out one stick, no changes. Im positive it was this update that did something..

So can you guys help me out? I really need it.

Specs if needed:
AMD Phenom X4 9950 Black Edition
MSI K9A2 Platinum Mainboard
ATi 4870 512MB DDR5
Apevia Warlock Series 900W
4GB (2 2GB) Corsair XMS2 800

**Tested another GPU, no success
**Tested another GPU in different PCI ports, no success
**Tested original GPU in another PCI port, no success
**Tested with just one stick of RAM, no success
**No beeps or unusual noises. Computer makes exact same noises as if it were powering up fine, just no display even though monitor activates when computer turns on/