My external hard disk 300 Gb can`t be opened

my external hard disk 300 Gb can`t be opened and it shows this error msg when i try open it : ( insert a disk in removebale) , also in his propreties in management disk  0byte).it can`t be detected by any computer or lap tp .i am trying with- jet flash recovery on line- i am flowing all steps but when runing the software it say please plug in your drive. otherwise, your device may be unrecognizable ,please take it to your nearest transcend store or contact). please if there are some ways to resolve my hard disk damaged or to recuperate my files in there which are very important to me ..so please help me...