PC playing up

I actually have the same graphics card you have.....the Leadtek Winfast A6600GT. If it crashes on the Video Card's BIOS screen....then I suggest you unplug the power and reseat everything you can and then try it again.

So there aren't any POST codes that emit when your PC fails to boot? What usually happens when it fails to boot? Does it just hang at random points in startup or does nothing happen? If nothing's happening, or it seems like nothings happening, then your Video Card is probably at fault. What kind of PSU do you have anyways? Because I know the A6600GT uses auxiliary power from the PSU.

Alternatively, if reseating everything doesn't work, do you have another computer to test the parts in question? Because that would determine whether or not your Mobo is busted.

I doubt your sound card is the culprit though....Your sound card being busted only gives you no sound. It shouldn't completely screw over your computer starting up.

Jam it back in, in the dark.