Wierd graphics problem on Windows start up

The problem started a couple days ago. I would start my computer and everything would be fine until after the “Welcome” screen on Windows. When the desktop should be loading, the screen would instead turn into a garbled pink mess. No input would work from the keyboard or mouse. I would have to turn off the computer and turn it back on. The problem has progressed over the week. Sometimes the screen would just go black. Sometimes I could hear the opening Windows chime although it was full of static. The last thing it did was give me a screen full of garbled colors and I was able to see a block instead of a mouse pointer.

My computer:

Windows 7 Home Premium 64 bit
Nvidia 680i motherboard
Intel Q6600
Nvidia Geforce GTX 280
Soundblaster Xfi
Intel 320 SSD boot drive
2x WD 250GB in stripe mode
Antec 1000 watt PSU

This always happens after the “Welcome” screen when the desktop should load.

If I hit the restart button instead of power button the BIOS will not POST. BIOS has most recent update.

Safe mode always works perfectly.

If Windows manages to load in normal mode it will work perfectly. I can watch movies, play games, do whatever. I can leave it on overnight and use it fine the next day. As soon as I turn it off and turn it back on, I'll start having problems again.

So far I’ve tried installing the GTX 280 in a different PCIE slot but it didn’t change anything. I tried installing the GTX 280 in a different computer and it worked perfectly. It worked with the windows driver and with the newest nvidia driver. The weird thing is that I tried the other computer’s Radeon 5870 in my computer and it also worked perfectly. It worked with the windows driver and the newest AMD driver. When I put the GTX 280 back in, it went to crap just like before.

The other computer that works:

Windows 7 Home Premium 64 bit
Asus P6T Motherboard
Core i7
Radeon 5870
Soundblaster Xfi
WD VelociRaptor boot drive
Maxtor 1TB storage
Same Antec 1000 watt PSU