The real-time clock (RTC) on a computer is a circuit integrated into the computer's motherboard that keeps track of the time and date, even when the computer is turned off and unplugged. The RTC is powered by the CMOS (Complementary Metal Oxide Semiconductor) battery. In older computers, this battery can lose power and may cause RTC errors until it has been replaced. In newer computers, the battery should not need to be replaced. In either case, follow the following steps until the error has been resolved.
Restart your computer. This often clears the error.
Remove any new components or peripherals you have added to the computer since the last time it was turned off. Unplug the computer before removing the case to remove internal components. Replace the case, plug in the computer and start the computer. If this has resolved the error, the new components are incompatible with your motherboard and may need repair or replacement.
Unplug your computer. Open your computer case and look for the CMOS battery. In older computers is should be a small removable battery, resembling a watch battery, attached to the motherboard with a clip. If the battery is not removable, skip to Step 6.
Replace the battery. Close the case, plug in your computer, and start the computer. Set the date and time if prompted.
Turn off the computer and wait five seconds before turning the computer on again. The real-time clock should be operating error-free.
Take your computer to a technician if none of the above steps have resolved the error. The motherboard will probably need repair or replacement.