I am at my wits end on this problem. all new games will load and play normally but certain games which are two or more years older such as left for dead 2 and Medieval 2 Total war will load but random polygons will be missing in the enviroment. Ex. a car will have random polygons missing out of it but will still work perfectly fine. Another ex. a persons face will be complete except for a triangle shaped part of his cheek which is missing. My system runs Windows Vista premium, my video driver is an up to date ATI Mobility Radeon HD 3400 Series. Thank you guys so much for your help
Have you tried removing your drivers completely, and doing a "clean" install? I have had graphics problems in the past that were remedied by doing a fresh installation as opposed to just updating to the latest driver.