Clearing the CMOS is a
High-Risk maneuver; and even if the OP has advanced tools to backup his CMOS, it might leave his computer unbootable!!
If you decide you've tried everything else, this should be a last resort approach! AND, make sure go into your CMOS BIOS first and write down every single setting on every screen possible; this is typically 60-200 settings and it can take an hour or two to do this with pen or pencil and paper. Alternatively, you can get out your Camera Phone and take pictures of each and every option screen first. If your computer still won't boot, you can go back into CMOS BIOS and reset all your settings to their original values from your notes or your photos on your phone.
If it still...