PC Not turning on. Nothing at all...

Right, so I had this problem http://forums.techguy.org/hardware/457389-usb-over-current-status-detected-2.html and one of the suggestions was to unplug it from the power supply. Well, since then, the computer won't turn on. No fans, no light (except the tiniest flicker when the power button is pressed). When my speaker was turned on, it made a short, loud beep/buzzing noise when the power button was pressed.

It was built for me by a friend (who is on holiday!)
Specs are:
Core 2 Quad Q6600 (latest revision G0 stepping)
EVGA 8800GTS 640MB Graphics
Antec P182 Case
Samsung SpinPoint 500GB Hard Drive
Asus P5K-E motherboard with built in wireless
Tagan TG530-U15 530W modular power supply
NEC 18x DVD-RW
Logitech LX710 Wireless keyboard and laser mouse
Crucial Ballistix 2GB 1066Mhz memory
Arctic cooling CPU cooler

Any help would be greatly appreciated, as this has come right before my final deadline for final year at uni. Typical...

Thanks