|So then you are sure you are talking about a BIOS password. |
So when you try to enter the BIOS (setup) you get this empty box?
Then first check the settings and mark down the values for the ones you don't understand so you can reset them the same. Then clear the CMOS with the jumper or motherboard battery removal. This procedure must be done with the power to the motherboard completely off. Some board manufacturers even instruct to disconnect the 20/24 pin power connector from the PSU.
After clearing the CMOS you must immediately enter the BIOS on the next boot to reset the values as needed.
That should rid you of the password prompt.