As fo3nix said, the most common way of clearing an `inadvertantly' set BIOS password is to remove the battery or alter the jumper settings.
When you did this, did you shut off the external power to the PC, you must do so.
The battery only needs to be removed for about 10secs.
Alternatively, enter the BIOS and reset it to `Default Values' which might clear it but you will then have to re-enter all your setings.
If all else fails, there are programmes available which will remove the password from the CMOS PROM chip but these can be a little dodgy and will depend upon which mobo you have.