First off, unless you have warranty on that 9800Gt, I strongly recommend upgrading to an ATI card. The equivalent of your 9800GT would be around the HD5670/HD5750. ($85 and $120, respectively). However, the best-deal on any ATI card right now is the HD5770, priced at a mere $140.
If you do choose nVidia, I recommend not updating your drivers. nVidia's latest drivers have burnt several tens of thousands of graphics cards; you are not alone. The drivers prevented the fan from functioning on the graphics card, which caused massive overheating.
As for BIOS settings; your PC will only shut down if your process (CPU) reaches above a certain point, I think. The default is 65'c, I believe.
Thanks for the Reply. I have given my card to my dealer and am hoping for a replacement in 15-20 days. Secondly Please suggest a software.
Also what is the ideal cooling required by a 9800gt. Thinking of going for a new case. Should Cooler master RC310 With 2 120mm Fans be enough.