Computer crash HDD or GPU?

Hey guys,

I've got a home built system that has been generally well behaved, recently however I have been having a problem where suddenly the screen will go blank. The sound continues to function for approximately 5 seconds before it also crashes and loops about a second of sound. After this the system will restart itself but this time with no video, and with a fan on full power, the HDD light flickers as though Windows is loading behind all this, it's just that I can't see it. To get it to work again I have to unplug the tower and then ground the motherboard before plugging it back in again. These crashes appear to happen at random, and I have two main suspects at the moment. The first is obviously the Graphics card, as it appears to be a video problem. The other is the HDD which is quite old, has failed S.M.A.R.T. tests and gets quite warm (63 deg). I have cleaned the graphics card fan of the considerable dust deposits, but am unable to cool the HDD properly atm.

Any Ideas?

Cheers