Hi again,
you can try and kick in the back-up BIOS
1. Turn off Computer by shutting down the PSU from the wall socket
2. Hold case power button in and turn on the power supply at the wall socket.
3. As soon as board shows signs of life turn power off at wall socket again.
4. Turn the power on at the wall again and then press the power button on the PC Case.
Now, I have to say that this procedure isn't always successful and you may have to try it several times before it works (it may not so don't be surprised) but, if it does work for you then you should get a message on the screen saying something like "Writing Backup BIOS to main BIOS DO NOT turn off the power" or something along those lines (sorry, I can't remeber exact wording). Once back-up bios has been copied you should be able to restart the PC and then enter BIOS to make changes as appropriate.
If this procedure does work remember that you will have the original BIOS back and, if you have upgraded your CPU, the original BIOS might not support it.