|Without knowing exactly when and where you are seeing this message I would guess the CMOS battery on your motherboard has gone dead. |
To verify this enter the BIOS (setup) screens when you first boot up the computer. If the date is wrong then the battery is dead. The battery is a quarter sized coin shaped silver battery mounted on the motherboard in your case. Unplug the compute before removing the battery. Pay attention to which side faces up before removing. Install a new battery in the same orientation.
When starting up for the first time after replacing the battery you MUST immediately enter the BIOS (setup) screens and reset values such as date, time, boot order, etc. Save when exiting.