I recently installed a new ati radeon 9800 pro graphic card to replace my nVidia geforce 3 ti 200. REALLY NICE GRAPHIC CARD!!! if i only had 8x agp

instead i have 4x which is the minimum. I set everything upright supposibly. I started playing call of duty and is lasts for like 30 seconds in the game and it crashes. Every single time i play the game it crashes. Even in some of the less graphic needy games such as natural selection (half life mod) dont work. I dont think the comp is overheating cause i set my bios up to shut down at some extremly low temperature.I'm pretty sure im running a 290watt power supply. I installed sp2, latest catalyst driver, 512 ram, 1.47 ghz athlon procesor and a 7200 rpm hard drive. I even called up ati but they didnt help. They gave me what they thought was the solution and hung up. Does anyone know why this happens? And would it be a better idea to just return it and get a nVidia geforce 6600 agp?