I hope you have a backup. If you don't, buy an external HD IMMEDIATELY, and back up. If need be, copy for an hour at a time, then shut down for an hour. Repeat as needed until all your data is backed up.
Get a new drive. Install OS as needed, copy all of your data onto it. Restore from your backup, or from the old drive an hour at a time.
Everything copied across, as well as backed up on the external? Good. Disconnect the suspect drive and run from the new drive for awhile. If the symptoms all go away, you'll know the old drive was at fault. Dispose of it in a humane fashion. Or violence can be therapeutic ...
If the symptoms do not go away, there's something else wrong with your computer. That is a separate diagnostic, but at least your data is safe.