Drive curpt and ask for format

Test the drive with the manufacturer's diagnostic software. The links are here:
http://www.tacktech.com/display.cfm?ttid=287

Check your drive by running Error-checking:
Randomly right click a partition in “My Computer” to select “Properties”=> Open “Tools” tab and hit “Check Now”.
This tool always can automatically fix some drive problems for you.
If this doesn't work, you could firstly run a free drive recovery tool to get your data back and format it to make it workable as before. I got this freeware as my drive was inaccessible last time. It was great since it had recovered all my wanted data back. So, it will help you, too. Go try it!