Problem with Invalid System Time

Hello,
I own a compaq nx7000 laptop with windows XP. I have recently encountered an "Invalid System Time" alert pop-up message box appears everytime I login.
The message is as follow:
"The time or date on your system is invalid. Please use the date/time applet in the Control Panel to properly set your system time and date."

After changing the time system, I did a virus scan but found nothing. Now, whenever I log into the Windows, the system time keeps on changing back to "January 1980 12:00AM" and the above mentioned message box keeps appearing.
What should I do to resolve this problem?
Please help.

Thank you.

check all batteries -- one or more may be low which will cause it to lose the clock time

There is only one battery that controls the time and date. The BIOS battery. If the computer is new, this SHOULDN'T but could be the problem. Instead of opening up a laptop which can be a hassle, plug the laptop in and restart it. With power to the motherboard the clock should not reset. Then restart it without being plugged in.