For some Asus and Gigabyte boards, for an easy cmos reset, press continuously the Insert key on your keyboard while powering up.
1. Press Insert key repeatedly
2. (while pressing Insert repeatedly) press the power button of your computer.
If it works as intended you should see the POST screen indicating that "overclocking failed".
If it doesn't you may need to reset manually with the cmos reset jumper (see your motherboard manual).