Thanks for your help. I'll do that and replace the HD, although scan within Windows showed it to be fine.

That error refers to the hard drive failing - not the SSD.

Before the drive fails completely, make a set of recovery media if you haven't done so - -you will need it once you replace the drive.

You will also need a backup of all your data that's on the hard drive, as it will be lost when you replace the failing drive.