R3000z will post from 2 -15 sec., then shuts down

That's the problem, took it apart, soldered the dc in, (was done before).
Suspected something else, because there was power on the battery charging contacts in the laptop from the start.
When on ac and with the battery in, the power led lights up about 6 seconds, goes off, goes on for 6 seconds again, then off, etcetera.
When powered up, I get anything from fans spinning for a sec., till the compag logo, push escape, and get to postscreen with memory count, hardware blabla and even sometimes to a bootsequence screen, with the colourded options floppy-hdd-cdrom. But it always shuts down before going any further.
Did the usual things, changed memory, applied new thermal paste on cpu.
Took all the peripherals out, hdd, dvd, modem, wireless. Tried it with a monitor (seems bad/loose lcd cable will halt posting too)What else can be wrong??? Some mosfet crapping out?