External hdd WD won't start

Hello, i have problem with my external hdd, western digital 320 gb. I have had it for almost a half of year. Eerything was normal until When I want to check my data yesterday, the hdd didn't want to start altough i have connected it into my computer. I can feel the harddisk is rotating and the indicator LED is light up, but it still didn't want start. It didn't show up in My Computer. (i'm using vista 64 bit). Help me to fix it please...