Remove all the batteries, look under the keyboard and covers to wiggle and re-seat any part or connector you can and then put it all back together and power it up with the AC source.
Still dead? Then it's time to consider repair or replacement.
I have a Compaq 1200 series laptop, about 3 years old or so. Last week, it was having trouble with a virus or spyware and eventually wouldn't let me do anything. It would boot to the desktop and then none of the programs would work (I'd get an error message if I tried to open anything). Even "Easy Restore" failed. Eventually I used the Emergency Restore Disk to bring it back to factory settings, and it worked fine for a few days.
Suddenly, in the middle of me surfing the web, the computer froze. I restarted, and it wouldn't boot. It still won't boot. It just sits on the "Compaq" screen. It won't boot from CD or disk. If I hit "F10" it will say "Entering Setup..." and then just sit there, but it won't actually enter BIOS.
I've tried unplugging it and removing the battery and holding down the power button for 30 seconds. I've tried booting it every way I can think of. I have no clue what would cause this, unless the boot disk is completely corrupted. HELP!