9860 random reboots :( HELP

my 9860 shutdowns randomly off late..like somtimes when i am playing some games or when i remove the power and try to move the laptop powered on..or sometime just when browsing the internet..a couple of times it even shutdown when doing post checkup...

i was just searchin some threads based on my problem and i must say i did one of those prohtbited things..i cleaned my laptop fans and vents using canned air!!which sombody pointed out that it could be bad...and coincidently this shutdown issue poped roughly after i did this foolish thing...

what could be the problem??
1) the canned air(dust from the fans and exhaust might have gone further into the hardware, as opposed to be cleaned)..
2) some driver issues (in compatible drivers)
3) some laptop power issue (the main connection of the battrey and ac adapter might be faulty)
4) over heating of cpu or gfx card

I have tried reinstallin winxp pro and 64 bit editions..updatin to catalyst 5.10..even using the old default drivers that came with the laptop whn i bought it..

i even monitoerd the temperature using getthermal...whn i ran getthermal 1st after rebooting problems arose..the temperature of cpu started at 40..slowly started rising till 70..i freaked out and enabled SetON and maxed out the fan speed..the temp then went down..

so what could it really be??

is there a permanent way to set the fan speeds at the max speeed or whatever user defined speed?? ..coz when i try it with getThermal,,after reboots it resets back to the default settings