Hmmm,

Fn-F3 Turns the display on/off
Fn-F4 Is suspend
Fn-F5 Is LCD/CRT

You might try them all.

Holding down the power button will just turn the PC off.Try pressing it once and also try the spacebar and "enter" key.

If you are running Windows 98 or later the BIOS power settings will have no effect.

Try hitting the Del key on startup to see if you can get into BIOS setup. I would guess that the battery needs recalibration. Also check the CMOS battery.......... strange things can happen if that is flat