I have a Dell Precision M6400 WS. Push power button comes on for about 3 seconds and shuts off. tried with battery in and...

Replace the old logic board with a new one !

remove the cmos jumper wait 10 seconds and then return it should work Update: remove the cmos jumper from the mother board wait 10 seconds and then return it should work. Also can disconnect the cmos battery wait 10 seconds and the reconnect that should do it also.