Hey there,
It's unlikely that all your drives are bad... But, then, it could be an issue with your tape library, if you have one. I've had issues where a couple of my drives showed as down, but upon closer inspection (literally going to the library and looking) I saw that I had two tapes occupying the culprit drives. I had to manually eject them from the library's console. You may want to power down the library bring it back up and then restart the server. Those are just my suggestions.