Stumped - Old Latitude D410 won't boot up, boot from CD, just black screen, no text.

Anyone know why a long reliable Dell Latitude D410 would turn on and seconds later turn off?

--without displaying the Dell logo

--without text or a cursor on the black screen

--without the ability to enter BIOS (or hit F1, F2, F8, F12 etc)

--without ability to boot off CD to run Dell Diagnostics Utility or re-install Windows?

Stumped, I bought a new (used) mobo. But after carefully installing it, I got same result - dead, turns on turns off without CD drive being powered or fan coming on.

It does have power, as shown by the farthest right of the three little green lights.

Any ideas?