Graphics card mysteriously died in the loft

Second question... So while I decide what to do about son's current PC, I've reinstalled his previous one. As far as both of us recall, it was working when it was put in the loft. However, now, I can get nothing out of the GTX510 (or GTX520) graphics card. It works fine off the onboard VGA port, but nothing out of either of the DVI ports on the GTX. Any idea why? The only thing I can think of is there's an option in the BIOS I need to change to get the PC to 'look at' the GTX board and not the onboard graphics - but it seems strange that this option appears to have reset itself in the BIOS while the machine was in the loft. There's no reference to the GTX in Device Manager, btw. Anyone have any thoughts?