CLRTC is usually a jumper on the board, look in your manual where is is (and how to use it).

Do not forget to turn the power supply off and remove the battery, also press the power button on the PC to make sure there is not charge left.

If the BIOS is cleared he BIOS screen will appear when rebooting, otherwise press the DEL key.

Load defaults will be under EXIT > Load setup Defaults.

No need to reinstall OS

Rob