My Book Won't Let me Add files

I got my drive last year and used it to save pictures ,files etc. Today I turned it on and tried adding files to the drive and the stop sign pops up. So I click the WD icon and it says Installation canceled, Unreadable WD SmartWare Drive, it goes on to say there is no writable WD SmartWare partition available on this WD drive. When I first used the drive I never installed a program, I just added my files. Can someone please explain how I can get back to normal and use to drive again. 


Check on disk management to see if the drive is being recognize

Unit might not be fully detected by the computer