You could try resetting the BIOS, there may be a jumper on your motherboard to accomplish this or you could pull the battery off the board. It looks like an oversized watch battery, carefully remove it with the computer powered down and unplugged. Then hold in the power button for about 10 seconds and put the battery back in.
When you turn the computer on press F2 (It might be different but it should say press X button to enter setup or BIOS) Set the date and time and see if that helps.