I am guessing that the harddrive is failing, just for safe measures, you should backup any important files/folders
Can you try the following, download Seatools for Windows diagnostic tool
from this direct link
http://www.seagate.com/staticfiles/support/seatools/SeaToolsforWindowsSetup-1204.exeIt's a diagnostic tools for Seagate and Maxtor drives, but shoud work with Samsung also
Run the installer, then from the desktop run Seatools for Windows
After scanning for your drive click "I Accept"
Put a tick next to your drive, then under "Basic Tests" select 'SMART Check'
Let the check finish, let me know if it passes or fails
Next, again select your Drive then "Basic Tests" select 'Long Drive Self Test'
This test can take some time, let me know if it passes the test