Perhaps, the drive file system is not compatible with the computer file system of your friend.
Is there something important data on this drive?
If so, you need a third-party data recovery tool to get back your data at first and format this drive to make it work well there afterwards. (Don't worry. There are many data recovery tools online. You should do some researching about "data recovery utility" and land a right one for your hard drive. You also could download a free data recovery tool to resolve your problem: http://www.raw-file-system.blogspot.com/2013/02/raw-drive-recovery.html)
If there is nothing important, you could straightly format it for its functional use.