Laptop switches off automatically within a minute

[Sandeepkuntam]

here are the symptoms... the laptop switches on for approximately 1 min and switches off again, the screen wont even switch on at all, the fan will run initially for about 10 seconds then switches off then again switches on for the last 15 sec before going off, the power light comes on when switched on but the processor/HDD light wont even blink, the battery and the HDD are working fine, DVD reader working fine, checked the RAM and HDD connections all fine, tried cleaning the fan its working fine.. i even tried removing battery and the power chord and pressed the power button for 30 seconds but the problem is still there.. please help...
Additional details :- the laptop was working fine till it went into a hibernate sleep when the battery reached critical level. after that i charged the battery and this happened tried using another battery but in vain..

 

[C12Friedman]

I'll suggest replacing the CMOS battery in the laptop.
Was the heatsink removed? If so, was fresh thermal compound applied (and any thermal pads reused or replaced)?