WINDOWS SERVER TIME

hi,

i am getting the fallowing event.

The time service has not synchronized the system time for 86400 seconds because none of the time service providers provided a usable time stamp. The time service is no longer synchronized and cannot provide the time to other clients or update the system clock. Monitor the system events displayed in the Event Viewer to make sure that a more serious problem does not exist.

This machine is my root domain controller. (FSMO ROELLER) but i am not facing any problems in m y network. pls suggest me.