Usually when it says that , it means something in the operating system is getting scrambled.
Do you have the recovery or an install disk?

If there is anything important on the hard drive , it would be good to copy the files to a flash drive , CD, DVD or some other storage device before or if a total failure happens.

Then if you have recovery disk or installation cd you could do a complete fresh install.

If the hard drive is making extra squeaks, squeals or odd noises then it might be the hard drive getting ready to fail.

Oh,
is the hard rive nearly full?
that can cause problems , if you can clean out/remove unused programs /files it may help the issue.