Can CMOS be replaced if it goes bad and how do you replace it?

If you are referring to a CMOS battery then it is very simple to install and cheap to replace. You can simply open your case and look for a very small, round silver item that looks like a watch battery only a little bigger. Remove it carefully and take it to your local Wal-mart and find a replacement that matches. To reinstall just pop it into place, and close the case.