Video card killed my computer

As things were working fine until the problem in-game I doubt drivers (or Windows 7) are your problem.

It is most likely that the video card has developed a fault (i.e. it has overheated somewhere by enough to burn out a component or few). If this is the case then hopefully it won't have affected anything else. To test the theory put in another card if you have a spare near by or can beg/borrow/steal one, preferably of similar brand and technology (i.e. if it is an ATI PCI-E card replace it with an ATI PCI-E card if you can).

Dieing this way may indicate that you have a cooling problem in your case (bad air circulation), or it could just mean that the card was a dud with a heat related fault waiting to be pushed over the edge by heavy activity and a little bad luck.

Windows 7 requires a decent video card to work properly with all the fancy Aero effects, and the default driver might enable DirectX effects instead of being a simple fallback driver.

Check the card for any visible damage; something may have been shorted or you may have blown a capacitor. If you can find it, contact the card's manufacturer immediately. The HD4830 is relatively new, and you may be able to get an on-warranty replacement.

If card has no visible damage, you may have corrupted the onboard BIOS of the card. Check to see if ATI offers a BIOS that you can use to flash the card (this might not be helpful if you can't get Windows installed).

Since your motherboard's BIOS got turned into gobbledygook, you may have corrupted that somehow. Remove the CMOS battery, unplug from the wall, press the power button 2 or 3 times, and let the computer sit for 10 mintues or so. This will reset the BIOS back to factory settings and may solve the issue.

If neither of these work, you may have borked the motherboard and the videocard. You'll have to get replacements.