DOS Password

Basic BIOS password crack - works 9.9 times out of ten
This is a password hack but it clears the BIOS such that the next time you start the PC, the CMOS does not ask for any password. Now if you are able to bring the DOS prompt up, then you will be able to change the BIOS setting to the default. To clear the CMOS do the following:
Get DOS prompt and type:
DEBUG hit enter
-o 70 2e hit enter
-o 71 ff hit enter
-q hit enter
exit hit enter
Restart the computer. It works on most versions of the AWARD BIOS.

Accessing information on the hard disk

When you turn on the host machine, enter the CMOS setup menu (usually you have to press F2, or DEL, or CTRL+ALT+S during the boot sequence) and go to STANDARD CMOS SETUP, and set the channel to which you have put the hard disk as TYPE=Auto, MODE=AUTO, then SAVE & EXIT SETUP. Now you have access to the hard disk.

Removing the battery
If you can't find the jumper to flash the BIOS or if such jumper doesn't exist, you can remove the battery that keeps the BIOS memory alive. It's a button-size battery somewhere on the motherboard (on elder computers the battery could be a small, typically blue, cylinder soldered to the motherboard, but usually has a jumper on its side to disconnect it, otherwise you'll have to unsolder it and then solder it back). Take it away for 15-30 minutes or more, then put it back and the data contained into the BIOS memory should be volatilized. I'd suggest you to remove it for about one hour to be sure, because if you put it back when the data aren't erased yet you'll have to wait more time, as you've never removed it. If at first it doesn't work, try to remove the battery overnight.

Important note: in laptop and notebooks you don't have to remove the computer's power batteries (which would be useless), but you should open your computer and remove the CMOS battery from the motherboard.
Short-circuiting the chip

Another way to clear the CMOS RAM is to reset it by short circuiting two pins of the BIOS chip for a few seconds. You can do that with a small piece of electric wire or with a bent paper clip. Always make sure that the computer is turned OFF before to try this operation.