8800 GT - No monitor signal

So I just built my new system at the shop a friend of mine owns. Tested it, installed vista (probably my first mistake). Got it home, fiddled with it for a while, couldn't get my Buffalo USB wireless adapter to work as their drivers are all outdated. So I shutdown, go back into town, get a wireless PCI card, and when I get back and switch it on there's no signal to the monitors.

Before I left I had it working fine with both monitors, was testing a few games and importing things from my old hard drive. And now nothing!

So, here's the specs:
GIGABYTE GA-946GMX-S2 motherboard
Corsair HX Series 520W Modular PSU
Intel Core 2 Duo E6540
Inno3D GeForce 8800 GT
2gb DDR2 RAM
Maxtor 250GB HDD (new)
Maxtor 160GB HDD (old one)



I've made very sure that everything is connected properly, wired properly and was working fine, but despite nothing being changed while I was out, it's decided not to work. Any help on this would be greatly appreciated.

Thanks in advance guys.