Thinkpad T22 Crashes

hi

i have a T22, and my laptop works fine most of the time, except lately it just crashs and the lcd goes blank. i can not even turn it off, unless i remove the battery and unplug the power cord. the screen goes blank, but i know that it also crashes because the light on the bottom of my mouse does away as well, and i am not able to get any response from the laptop no matter what butons i press. sometime it happen 5 minutes after i turn it on, other times it happens after a couple hours.
i have run antivirus checkers, spyware checkers, but no luck. anyone have any ideas?

thanks
john