There should be a jumper near the battery like the one pictured here (the right hand image, not the left).
http://www.villagegeek.com/techsuppo...er/jumpers.jpg Pull the jumper from the 2 prongs it is covering and move it to cover the center prong and the one to the opposite site.
For instance:
.. are 2 prongs not jumpered
_ are 2 prongs jumpered
If you pull the jumper off, you have this: ...
Move it from ._ to _. and reboot. You should get nothing. No lights, no nothing. Move it back to the original position, and the system will boot with a reset BIOS.
If you do not have this 3-prong jumper, you can unplug the system and remove the CMOS battery. Leaving the CMOS battery out for 5 minutes usually resets the CMOS. If not, then you will have to leave it out for an hour or so.