How to clear cmos in asus a7n266 mb - ASUS NVIDIA nForce Chipset A7N266-VM (A7N266-VM W/L) Motherboard

Remove the cmos battery and wait for 3 minutes and place it back...
Alternatively you can remove the CMOS Jumper present near the CMOS battery and place it back it will clear the CMOS memory...
To be more specific, if you do remove the CMOS battery and if you turn ON the system everything will be flushed in CMOS immediately...

I had similar mobo and this is what the Asus technician told me. Take out the round battery in your motherboard and flip it around and put it back into the battery slot.(it sounds weird but that is what he said) Hold it there for 20seconds and then put back in the right way it was.

Your cmos should be cleared now. Make sure your pc is switched off when doing this.