Hi 1st The clear bios / cmos button on the back how to use. Shut down pc leave power cable in press the clear bios / cmos button for around 30,secs turn pc back on that will clear the bios. 2nd the bios will keep the date & time because the mother board has got a battery in it have a look in your manual if you have not got one just google your (MB) Name for a manual you will find one no problem if you what 2 clear your date time ect. just remove the battery they look like watch/hearing aid batteries for around 1min replace job done when you boot back up into your bios the date time has been rest hope this helps let me no if u need any help