Posted 24 January 2011 - 11:42 AM
You enter the bios (Basic Input Output System) by entering one of the F-keys when you first boot up (turn on) the computer. If you shut down and power up again or restart, there is usually a black screen with some white writing on the bottom of the screen (possibly on the top) telling you to press one of the F-keys to enter SETUP (often F2 or F8 but different systems vary). Setup = bios. From there you can set date/time, configure hard drives and other hardware settings. etc.
Usually the opportunity to enter setup (bios) goes by very quickly, often less than a second, so you have to be ready, and possibly restart a time or two to figure out which F key to press and then to actually get it pressed in time for it to work. I wouldn't recommend messing with most of the settings there, but date/time are pretty straightforward.
Failing that, the cmos battery is inside your computer, usually on your motherboard. Typically they are a small silver colored button battery, maybe the size of a dime or so. Relatively inexpensive and easy to replace - as far a computer components go.
Good luck and let us know how are doing with this problem, or if you have more questions.