Blank screen after windows loads?

I opened up my PC to move the front audio cable so that it wasn't sitting on the graphics card (was causing EM interference).

When I tried to reboot, my computer now gets to the windows loading screen, then stops outputting video - so the monitor goes blank and eventually turns off. Windows continues to load in the background as I can hear the startup sound play.

Any ideas if this is likely to be a hardware failure / software failure?

Computer Setup:
Gigabyte GA-EX38-DS4 Motherboard
Intel Core 2 Duo E8400 CPU
Gigabyte 670 GTX Factory OC GFX Card
4GB RAM (I think XMS2)
500GB Samsung Spinpoint F3 7200rpm HDD
Corsair 650W modular PSU
Linksys PCIE wireless card (can't remember model)


Things I have tried:
1) Booting into safe mode (works fine, can view the desktop etc.)
2) Booting into low resolution mode (doesn't work, same issue)
3) Booting into safe mode, un-installing the graphics card, booting into normal mode and reinstalling drivers for graphics card (doesn't work, same issue)
4) Trying a different PCI-E slot (doesn't work, same issue)
5) Trying a different output on the graphics card (doesn't work, same issue)
6) Hard CMOS reset (doesn't work, same issue)
7) Trying a different graphics card (even worse, didn't get any video out even at BIOS screen - can't guarantee card is working as I don't have a second machine to test with but it was working the last time I used it a couple of months ago. Second card was ATI rather than Nvidia so shouldn't be using same drivers).

Things I intend to try but haven't had time:
1) Plugging into a different monitor (heard some people mentioning it may be to do with the monitor drivers not reporting max screen settings properly, I could find any windows 7 x64 drivers for my monitor as its so old but I do have a TV I can test with)