After powering off the computer and switching it back on after a few hours, the time has changed
Cause: The CMOS battery powers the real-time clock. This symptom indicates that the battery is dying. In rare cases, it could also mean there’s a problem with the battery port of the CMOS.
Solution: Replace the battery. If the symptom persists, there’s a good chance that the battery port is damaged. In this latter case, you may need to replace the motherboard! Get it checked by a computer technician first.