Try another server.
Open up the clock.
Copy this tock.usno.navy.mil
then paste it into the server box.
Open the clock back up again, choose tock.usno.navy.mil
from the drop down menu if it doesn't show in the server box,
Maybe both the servers you tried are down.
Another thing to try:
net stop w32time
net start w32time
(if unregister tells you access denied, go to the next step)
Try synching with the server.
As hamluis stated, it is possible that the CMOS battery needs to be replaced.
Edited by Queen-Evie, 14 August 2008 - 07:35 PM.