Could you find it in "Disk Management"? How is it displayed there?
If it is displayed in "Disk Management" without a letter, you should assign a letter to it and format it for activating it on your computer.
If your drive has stored something important, you are supposed to select a free data recovery tool to rescue it before you format it. (I have tried this freeware to successfully recover my important data from an inaccessible drive. It is fantastic. You should try it personally.)