bios

AMD +2100 WINDOWS 98ES I set bios seting and date, time 01/24/2003 the BIOS GO BACK TO Default setting after I shut down my computer 1 to 5 min. AND computer boots up after power on.
computer shows date, time CHANGE BACK TO 1/1/2000 How do I FIX THIS.
If I REBOOT ALL IS OK. But if I shut down it go back to Default .