dell d630 video chip temp sensor

 the moment I power up, the fan goes to full speed and cpu throttles back 87 percent. the sensor page shows tr1 is jumpy and tr2 is pegged at 265c. the video seem to work fine. I am controlling the throttling with windows performance settings and bios power settings.  I believe the video chip is fine but I want to repair the sensors. I running windows 7 sp1 32 and have done fresh install of bios A19 and windows 7. I also installed latest driver from NVidia. I also have I8kfan controlling the fan. all other temps perfect. thanks for help.