How do I reset the CMOS?

All motherboards will have a flat CR2032 button battery located on them as shown above, some will be difficult to reach with other hardware such as GPU's installed so will also have CMOS reset pins, these can be labelled with either JBAT1, CLRTC, CLR_CMOS, CMOS_RST. If you can not find the CMOS reset pins consult the manual as the name of the pins may vary by manufacturer, more modern motherboards may have a CMOS clear button on the rear IO of the motherboard so you do not have to open the case, If you are using the button reset we would recommend consulting the manual or product page for further information on how to do this as it can vary by manufacturer. 

Removing the CMOS battery
If you can access the CMOS battery fully power off the PC and switch the power supply to OFF, you can leave the kettle lead to the wall plugged in if you wish however if your power supply does not have a switch so you can turn it off it will be best to unplug this. 

Once you can access it, remove the CMOS Battery from the motherboard, usually this will have a small metal spring clip on it that can be pushed out of the way and the battery will pop out. Sometimes there will be a small piece of rubber or plastic in the clip to prevent it from accidentally being pressed this will need to be removed before pressing the clip in to release the battery.

Press and hold the power button on the PC for at least 15 seconds, nothing at all should happen, which is what we want. 

Re-insert the CMOS Battery, and the GPU if removed, and turn the power supply back to the ON position,

Press the power button on the PC to turn on the PC.

Reset pin method

Fully power off the PC and switch the power supply to OFF, you can leave the kettle lead to the wall plugged in if you wish however if your power supply does not have a switch so you can turn it off it will be best to unplug this. remove the side panel from the case and locate the CMOS reset pins on the motherboard.

Once you have found the CMOS reset pins use the tip of a screwdriver or a conductive item to gently press against both of the pins bridging them to discharge the motherboard. You will need to keep the pins bridged for a minimum of 10 seconds before setting the PC back up and testing.