There could be several causes for this problem.
Things to check:
Have you backed up all your data? It may be the HDD that is failing.
Is your clock changing/losing its setting? The backup battery could be flat.
Can you get into BIOS and check your settings?
Do you get any other messages at boot such as boot.ini not being found?
Does CHKDSK run at start up?
How old is the PC?
Have you checked Device Manager for any warnings?
Have a look at these and let us know what you find.