If you want to recover data from it, DO NOT Format or Install anything!!
treefrog07 said use the WD Data Lifegard free diagnostic utility package from WD's website. Do that for sure. My own preference is to download the version that has you burn your own copy of it to a CD-R. You then insert that into your optical drive and boot from it. It loads a mini-DOS into RAM and you run all its tests without ever using you regular OS, Windows.
The test package is menu-based. Read its instructions and run its tests, noting down what it says for each. Sometimes you'll get messages that say it's hopeless, sometimes it will says it can fix the problem if you want it to. If you need to call WD Tech Support for help, having the diagnostic tests' messages written down will help a lot.