Assign a drive letter if you did not. Then reboot, if still no luck right click the drive in My Computer and choose properties then tools, then check now and scan the disk for errors.
Also when you formatted did you make it a primary drive? If not format it again and make it NTFS and Primary
You may just need to get into DOS and use a DOS utility to set the drive active, without a drive being active you can see it but not use it properly. You can also do this within windows using Paragon Partition manager.
Or get a A Ultimate bootcd, which has many partition tools all of which can do this option.
Or you can see if the vista feature that does this will work, I have never used it and always do in DOS or a goof partition app >>>>
Right-mouse on My Computer->Manage->Disk Management. Select another drive
(not C....So select the drive in question here) and rightclick and select "mark partition as active".