Random Shutdowns due to Overheating

Hey guys,

I have an overheating-shutdown problem on my Dell INSPIRON 15R N5110. This happens exclusively when playing games. I used to be able to play all the games without any problem as recently as 2 months ago, but I laid off them due to work. Now however, after about 20 mins into any game - even older games like half life 2/portal/bioshock, I would notice the areas around the fan on the left hand side, as well as the area near the left mousepad getting really hot to touch and after a couple of minutes the laptop would just abruptly shutdown.

I thought this may have been a 'dust' issue with the fan, but I had a look at it with a torch(too finicky to open whole laptop - no fan panel) and I cannot see any dust and the fan seems to be moving freely and making the same amount of noise as usual. There is sufficient ventilation as its on a hard surface. I have run several virus scans and they come up clean, ran several "Dell Diagnostics" on the startup screen and all the hardware components seem to be working fine and all the drivers are upto date.
Even after all this I still cannot figure out what is wrong with this laptop. So any help on this, as well as what my next steps should be would be greatly appreciated. Thank You.

SPECS: Inspiron 15R N5110
WIndows 7 Home- SP1
Intel CORE i7-2630QM @ 2.00 GHz
RAM: 8 GB
Graphics: Intel 3000series/ Nvidia GT525m 1 GB 
Hard Drive space: 223/500 GB left
Warranty expires 2014- so I can get something done professionally, but it would take about 2-3 weeks (wholly undesirable since I use it daily)