possible laptop motherboard damage

i own a toshiba satellite l20
It is not turning on and i suspect it is something to do either with the bios battery or the motherboard itself. The leds blink for 3 seconds and turn off.

The laptop is out of warranty and i dont use it. But, if it can be repaired, it would be great. I actually want to try repairing it without going to the service centre as i dont want to waste money on it.

What can be done to diagnose the problem??

I have checked ram, battery, lcd , hard disk and also found bios battery voltage as 2.5v

Please help

I ci have no issues in dissecting the laptop.

update:
Before it went dead, i just changed the ata channel mode from pio to dma as it offered significant performance improvement. Can it have something to do with the problem.