Dell Studio 1555 shutting down

Hello guys. I have a problem with my laptop. Dunno if it is hardware or software problem. My laptop keeps on shutting down when i use OpenGL in Counter Strike 1.6, i fixed this problem by using D3D mode in the game. Another problem appeared when i installed NFS Underground. I dunno why the problem with the laptop sudden shutdowns appeard again. This problem doesn't occur when i play League of Legends for example (game runs ar high setup). Seems like it isn't a heat problem, non the less i can't figure out what is happening, so i wonderd maybe you can help me solve this.

That's the problem, i don't get a BSOD. Computer just power off's. After i open the laptop again, it says just that the windows has not been shut down properly. That's all the information i have. And btw, in Event Viewer i don't see errors or things related to it.

I just updated my ATI drivers to last driver 11.5, hopefully this solves the problem. If not, i will come back with a reply.

So far so good. It seems like the update fixed the problem but i dunno for sure. if the problem reappeares i'll post again.

It eventually seemd like the crashes were most probably from the ATI Display driver version 11.4. After i uninstalled the driver, restarted the laptop and installed the new driver 11.5 the problem seems to be solved, now even the CS 1.6 in OpenGl mode seems to work flawlessly. Anyway thank you for your support. If the problem persists I will eventually return for more debugging procedures. I also made what you said. Hope it will help at next crash.
Thx for help,
Sincerely Andrei.