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Sounds like an overheating problem off hand, you can monitor your temps with Coretemp (available free here) http://www.alcpu.com/CoreTemp/
Are you sure the exhaust fan is working? Do you feel warm air being blown out of the side vent from about 3"? Was it disassembled and cleaned (best) or cleaned with compressed air?
You can also use a cooling pad like this http://www.newegg.com/Product/Product.aspx?Item=N82E168...
to help control temperatures also - if that is the issue.
See what coretemp has to tell you...
i recently bought a acer 7750g laptop and it keeps shutting down after 5-10 min of play time, i wonder what can be the problem? i cleaned everything in it the vents and all the dust is gone
Check the BIOS version. I flashed mine to 1.20 to see if there were general improvements. I was a little disapointed when I found that this version would not manage the system fan anymore resulting in temps close to 100°c. According to Acer service specs for the 7750 series the machine shuts down on itself when reaching such temps.
I flashed back to 1.18 and got everything working perfect.
I have 7750G-6645 with 7670M gpu. I had this problem and have read that many others have had similar issues revolving around the switchable GPU. I too would bluescreen every 5 mins about depending on the game (my temps were fine). I think what most other people do is use a modded BIOS so that they can disable use of the integrated card. I solved the problem for the most part by using 3rd party drivers from leshcatlabs.net. I also want to try the modded BIOS to see if i can get further improvement but I'm scared of doing this since I'm not that savvy with the process...