Gateway NV79 unexpected shutdown

My laptop is shutting down when i attempt to play any kind of game, even one as simple as runescape. I brought it in to be professionaly cleaned and when i recieved it, the problem remained. Speed fan records the temperatures getting into the 80cel before this happens tho. I've even tried putting it on a big square fan but it does not help..... it worked fine for months before this started happening, could it be the memory? the motherboard? please any help would be very apperciated, thank you.

OS Name Microsoft Windows 7 Home Premium
Version 6.1.7600 Build 7600
Other OS Description Not Available
OS Manufacturer Microsoft Corporation

System Manufacturer Gateway
System Model NV79
System Type x64-based PC
Processor Intel(R) Core(TM) i7 CPU M 620 @ 2.67GHz, 2667 Mhz, 2 Core(s), 4 Logical Processor(s)
BIOS Version/Date Gateway V1.05, 05/01/2010
SMBIOS Version 2.6
Windows Directory C:\Windows
ATI mobility radeon HD 5650 1GB
Installed Physical Memory (RAM) 8.00 GB
Total Physical Memory 7.87 GB
Available Physical Memory 6.30 GB
Total Virtual Memory 15.7 GB
Available Virtual Memory 14.1 GB
Page File Space 7.87 GB

You might need to have the CPU thermal paste replaced by a laptop tech