Dead HP Presario CQ62 notebook

I have a HP Presario CQ62 notebook that just totally died.
I closed it up after using it normally, came back and opened the lid and it was dead. No lights, not even power supply indicator light. Nothing happens when the power button is pushed of course.
I thought and hoped it was a faulty power supply and a flat battery, but I have a spare power supply so this was able to be ruled out.
Not that it's relevant here, but it's running Windows 7 64 bit.
Anyone got any ideas where to look for a solution to this? As it won't fire up on battery or power it has to be after those.

Remove the memory and re install it... Remove the battery and try AC power only. With the battery out and AC out, hold the power button down for 30 seconds. Re install the battery and see if the laptop powers up

Thanks, but didn't work.

The motherboard has gone bad. How old is the laptop?

The laptop is 18 months old

Out of Warranty...
Is this your motherboard:
http://www.ebay.com/itm/COMPAQ-PRES...therboards&hash=item1c23ab45dc#ht_4605wt_1163

Yes, it is out of warranty, although I am enquiring about implied warranties through the Australian consumer protection agency ACCC before I start taking it apart. If I'd bought 2 months later there would be no problem as they bought in new laws then that cover this situation. There are many motherboards for this model. I'll have to check which one it is. I have the repair manual which lists them all.