I have a gigabyte k7 Triton GA-7N400 pro2 board and I had to reset the bios. After this I found I could no longer restart. The computer will shut down fine and start from cold boot with no problems but if I press ctrl + alt + del or restart from windows the computer will shutdown and begin to power up but make it no further. Nothing appears on the screen and there is no POST beeps. I was guessing that there must be some setting in the bios but I nothing seems to fix it.

I've no idea. Maybe this is something the Gigabyte Technical Support can help with - http://uk.giga-byte.com/TechSupport/ServiceCenter.htm. That's the English version, but you can get to other versions from there.

If you are using windows xp, then you should be able to boot into Safe Mode and then do a "system restore" to return your system back to its previous state.