Crashing During Games

Recently my computer has started crashing playing video games.
The crashes are random and can happen anywhere between 10s of the game running, to an hour or two of the game running. The crash causes my screen to go black instantly, and my audio repeats a buzzing noise. It used to only happen on high-end games, but recently started happening to older games and low-end games. I've only got a few games left that I can safely play, and for now, I've just stopped playing them to prevent anymore crashes until I can find a solution.
It's not a heat problem, I've monitored the heat before a crash, and it's crashed without anything getting to 45C, whereas during highend games the GPU can get up to around 60C, with everything else being around 50C. I did clean it out just in case, but it hasn't changed anything.
I've also tried updating my video drivers, using an older video driver that had worked before, and even tried a beta driver out of desperation. I've also made sure I had the latest drivers for my bios as well.
Also, I've not made any hardware changes for about 6 months, and that was just putting in a new HDD.

My computer is a Gateway FX MS2252
It's specs are:
Windows 7 (64bit)
Nvidia 9800GTS (1900x1200 resolution)
4gb ram
Duo Core Processor ~2.3GHz
Here's a link for more detailed info about this model:
http://www.overclock.net/t/293505/gateway-fx-laptop-series-thread-mods-and-upgrades

The only solutions I've come down to is that my video card might be dieing. Is there anything else I can do to try and solve this problem, or is this laptop doomed to never play vidya again?

On a side note, I've noticed from posts on the web that some people have a similar error when a power supply isn't providing enough power(I'm almost always plugged in when gaming). Is it possible that my battery/power adapter is going faulty and isn't delivering enough juice? Or is this false hope?

 

What anti virus you using as well? as i find norton and kapersky takes more resources then they need even in just idle.
Has your anti virus got a gamer profile? if so try that.