Could be anything from replacing the cmos battery of the motherboard.
Or a motherboard chipset failure of the north or south bridge chips located on the motherboard.
Check that the cmos battery is not flat on the motherboard, if the time and date of the system is wrong as well as the year the bios battery or coin cell on the motherboard needs to be replaced to fix the problem.
A simple way is to enter the bios of the motherboard and check the time, date and year settings are correct.
It cost you about fifty pence to £1 to replace the coin cell battery. Cell number CR2032.