Blinking " ! " on taskbar says " A drive on this system reports it may fail". I went to web site and ran test. All good except "Reallocated sector count ID: 5 Value: 133 Threshold: 140 Worst: 133 Warranty: 1 ". This only drive on system.
Get the WIndows Data Life Guard diagnostics and try getting the results. I experienced this with my Caviar Black 1TB this past Dec. 2010. Any email correspondance with WDC Tech support requires the WinDLG results as they can not read any other results.