Whatever you decide to do, backup any important data that's on it to another drive or to optical discs (you should be doing that anyway, even with a healthy drive).
You may want to test it with
WD Data LifeGuard Diagnostic for Windows (I assume it's only a storage drive since it's partition letters are D & E):
http://support.wdc.com/downloads.aspx?DL
If the drive passes the extended test I'd have no qualms about continuing to use it (provided you keep it's data backed up as I said earlier).