|A desktop motherboard usually has a 'clear cmos' jumper. Sometimes doing that will clear a bios password also. With the power cord disconnected, locate the jumper on the motherboard. Jumper it to the 'clear' position for a few seconds then move it back to standby or normal. Then connect the power cord and start it up and see if that fixes it.|
Less likely but still possible there may be a 'clear password' jumper which you'd utilitze in the same way.
You may need to consult the motherboard manual to find out where the jumpers are located.