Sounds like a GPU problem...
have you cleaned all fans inside the laptop, especially the GPU fan?
If they are clean, is it possible to login to Win7 (after a few reboots maybe) and run this:
http://freestone-group.com/video-car...ility-test.htm
Do you know if the laptop has a MXM or MXM-II/III slot for the ATI graphic card?
If not and the GPU is faulty, maybe a reflow will help?