Alienware Aurora randomly crashes while playing games?!

So recently my Aurora started crashing while playing games for more then 15-20 minutes. It did it very often for a while, so I opened it up and cleaned the massive amount of dust that was inside it. It came up with an error message when I turned it on saying something like "Overclocking failed" and asked me if I wanted to ignore the changes (which I did). This fixed it for a while, but now it's starting to do it again. I'm not sure whether it is just dusty again (although the first time I cleaned it, it had over a years’ worth of dust!)

When it crashes, the screen just goes black and the sound loops. It crashes on games I know it can handle (Half Life 2, Team Fortress 2) Games that my far less powerful laptop can play with no problems.

I had a suspicion that it could be down to my version of Direct X (11) not being compatible with the games/my graphics card/the games.. But I don't really think this is the case.

If all else fails I'll just clean it out again (probably when I get access to a decent vacuum cleaner!)

Thanks for your time

Charlie