Dead e1505 question

Hi -

I have an e1505 laptop. About a month beyond the complete care warranty, the
thing just "blinked" off while in use. That's the best way I can describe
it. What happens now is, when I plug it in and hit the power button, the
power supply's green LED immediately goes dark. I can unplug/plug in at the
wall to reset the power supply, but the same thing happens when I try to
power up.

The battery (Dell) is new, and the power supply checks ok (also tried a
replacement). So, is the motherboard likely gone/shorted out? And if so, is
it worth replacing, I think they can be had for a couple hundred and I'm not
averse to taking the thing apart.

Thanks! - John