The CMOS Battery
The CMOS chip requires a small trickle voltage from a battery to keep its memory alive. When the battery gets low or runs out of current, the computer will experience a sudden memory loss and thus lose settings. The voltage of CMOS batteries ranges from 3 to 6 volts. These Batteries come as either on-board (NiCad batteries, soldered in place or in a fixture, that last from five to seven years) or external (No rechargeable AA alkaline batteries that last from two to four years).
Some time to load the default setting of the CMOS setup; remove the CMOS Battery for few mints and place it again on the motherboard. The first clue that the battery is weakening is that the CMOS clock begins to slow down. Go to a “C” Prompt and type time. If you notice the clock is slow, it's time to change the battery.
