XFX 8800 GTX not working in Windows Vista

My games are constantly crashing on Vista Home Premium. The old gpu that was installed in my system at the time of purchase was Nvidia 7300 LE. It was working quiet fine and there was no error. I was using Windows XP at that time. Later on I bought XFX 800 GTX for my system. I added it and it was fine. I got an notification for Vista upgrade. I performed the same. The upgrade when fine without giving any errors with all driver setup. But now when I run any game it crashes. A number of games lags a lot. I have 2GB RAM. Recently while playing Dungeon Siege 2 I faced a blue screen error. The erroe was STOP: 0x00000116 (0x9CBEBBA0, 0x8B6E29A0, 0x00000000, 0x00000002) / nvlddmkm.sys - Address 8B6E29A0 base at 8B6DE000, DataStamp 45e829.

This looks some kind of driver problem in your system. When you had added the new card did you found a compatible Vista driver for the same. It is quiet necessary that you must get the most compatible and appropriate drivers for the gpu. If possible you can try testing the gpu on some other working system. There can be hardware fault also.