Problems with Dell n5010 overheating

Hi,

I own a Dell N5010 laptop. It has performed very well for me so far. However, I have been having problems with the system crashing recently. It first occurred while I was playing DOTA 2 online. The laptop lost display and restarted about a minute later. While attempting to boot, it kept failing, losing display and restarting. I had to shut it down for a few minutes. I was able to get it back running but whenever I attempt to play a game (usually Skyrim or DOTA 2), the laptop crashes.

I have a habit of monitoring my laptop's temperature. I have that these crashes can occur between the range of 60 and 85 degrees (centigrade). This is baffling, since I remember getting temperatures of 90+ while playing Civilization 5. Even then, the system didn't crash, I got a warning of high temperature only. I bought a cooling pad that kept the temperatures below 80. I still have it and I uses it while playing a game on laptop.

I am not sure why the system is crashing. I have noticed that the system fan switches on and off by itself. I am not sure if it has done that always, or if that is the cause of system crashing. I have run a Dell Diagnostic and the results show that all components are perfectly healthy and running fine. I would really like to get some information on this problem and what is the best solution. Laptop information is given below:

Dell N5010
Intel i5 M460 (@2.53 GHz)
4GB DDR3
500 GB Seagate
ATI HD 4650 Radeon Mobility 1GB

I am new here, and do not know how to generate a report of system displaying all the information. If you require more information, please let me know.