Random Crashing during Portal/Portal 2/l4d2

Hello everyone,

I've been an owner of and Envy 14 since August and have just recognized a strange crashing issue while I play the mentioned games in the title. I am able to launch the games just fine, play for anywhere from 5-45 minutes, and then suddenly, the laptop just freezes and goes into a black screen, forcing me to manually restart. This happens every single time I try to play those games.

At first I thought that the laptop was overheating so I started monitoring my temps. When doing basic tasks such using word/internet/skype, the temp stays around 36-42 degrees Celsius. After playing Portal 2 (before it crashes), the temperatures spike up to the mid-high 70s. Are those temps considered unsafe???

What's odd is I can play Team Fortress 2, BF:BC2, and GTA4 for hours and not experience a single hiccup in performance, let alone a crash. Also, the temperature stays around 70-76 after playing those games.

I use a cooling pad and today I tried cleaning the fans (both inside and out) with compressed air; however, after launching Portal 2 today and playing for 15 minutes, the lappy crashed again...

Is anyone else having an issue similar to this? I just don't understand why some games that appear to be in the same gpu/cpu demands run perfectly fine for hours but others just randomly crash.

I appreciate any and all help on this issue. Oh, and here are my specs:

Windows 7 Home Premium 64-bit
i5-520M
4GB DDR3
500GB 7200RPM
BrightView Display