I shut down one of my two T42's and next time I tried to boot
there was nothing - no lights/leds anywhere, no beeps, nothing.
Tested the AC and its reading 16.7v, changed the battery for another
charged one but no sign of life at all.
What would be the first possible causes/problem ?
Thanks lots !

Let's try this old trick:

Remove the battery, hard and media drive, unplug the AC adapter.

Press the "power" button ten times in a row, holding it down for 10 seconds each time and thirty seconds the last time around.

Plug the AC adapter - but nothing else - back in and try to power on.

Good luck.

LOL, sounds more like ceremony and vodoo than anything else...

Not that I necessarily doubt it may work, there are a few things about computers that take magic fingers.

BTW, that used to be IBM's official procedure when you called phone support back in the days complaining about a still-in-warranty A20m that wouldn't power on...

Maybe for $100 I buy another one and just switch the
drives ?

I'll sell you a guaranteed working replacement motherboard for $60.- including shipping.
PM me if interested (also see my signature).

Well I dont know if I can get the case screws out.
The heads are very chewed up. I'll try later in the week
and maybe take you up on that motherboard. Thanks !