Post a copy of the SMART errors. Also what brand/model disk.
For Seagate use the seatools
For WDC use the wddiag util.
Pull a list of errors in SMART and lets see the overall health.
Some smart errors are benign or acceptable with super high power on hours, others are a sign of eminent failure.
I would recommend you backup anything you need on the drive ASAP (Outlook settings, etc) that normally get stored on the OS drive regardless of where you installed it to.