|Your CMOS battery has failed. That is the silver coin shaped battery mounted on the motherboard. When replacing unplug the computer first and take care to install with the same side up as the original.|
In the interim you can boot into the BIOS (setup) screens and reset the values. The settings will hold as long as you don't interrupt power to the computer. You can shut it down but don't use a power strip. Power to power supply will hold the settings.