External Drive Unreadable

I have a 1TB Seagate freeagent goflex which until yesterday worked fine (using a Mac). now when i plug it in i get the error message saying it is unreadable. In disk utility the drive shows up but no volumes are listed under it and i dont have the option to verify or repair. i tried several recovery appllications and when i finally gave up trying to fix the problem that way and attempted to erase the drive i got a message saying the drive can not be opened. hoping someone has had a similar problem. Ive had drives mess up before but disk utility has always solved problem.