Dell Studio 1555 graphics issues

I purchased a Dell Studio 15 last June, and since I have gotten it has yet to continually play any game. I have installed Call of duty 2, and call of duty 4. I can play call of duty 2 for about 30 minutes before I begin to have graphical issues. On the other hand, call of duty 4 experiences graphical difficulties immediately when i begin playing. The strange thing is though that I have played call of duty 4 without any difficulties. I have called dell and installed/reinstalled the drivers and it doesn't work. What else can I do?

I can't take a SS of the graphics problem for some reason, but here is a cell phone picture. You can see the black boxes. Lines in every color imaginable appear as well.

My specs are:

 

Power up HWMonitor (google it if you don't already have it) before you start gaming, and take note of the temperature, switch back to windows after 15 minutes and have another look and then finally when you start to see the graphics issue. How hot is it?

Also, when powering on the machine, press the power button and the Fn button at the same time to launch some diagnostics that will test the graphics. See if it displays any warnings / errors

 

It sounds like the GPU is artifacting, which is most commonly caused by heat, and if it isn't heat, it means that the GPU is on it's way out. Like Fragilexx said, download and install HWMonitor, and measure your temperatures.

Have you ever updated your drivers? That could also be the cause to this problem. Some drivers can cause graphical glitches, and various other problems.

 

Fragilexx, the top poster has already made another question at the gaming hardware board, so you might want to post there as well.