How to perform a CMOS reset
1. Power off the computer and remove the power cord from the PSU.
2. Locate the CR2032 (or similar) button battery on the motherboard. Bear in mind that they can reside behind the GPU or the CPU fan. In these circumstances you may need to remove the component to get access.
3. Remove the battery by using the lever seen to the right of the battery on the above picture. You will want to push it in the outwardly direction.
4. Now hold down the power button of the computer for 30 seconds.
5. CMOS reset is complete, replace the battery and boot the computer.