Yellow Health Warning...

I just ran a defrag and the word WARNING appeared in yellow to describe the health of my disc. Does anyone know what I should do about that...?

Thank you.

Is that the S.M.A.R.T. status? If so it could be the hard disk is about to fail/die so backing up all important files to external media (USB Thumb Drives, external hard disks, CDs, DVDs, etc.,) is something to start doing immediately.