Cheval_Blanc

Beeping of external HDD means loose wire or the the internal cable is disconnected/broken, it might due to aged, physical crashing, unsatisfied quality or poor preserving condition. It is impossible for you to run any data recovery tests since the HDD was unable to detect, the only one thing you could do is STOP connecting the HDD to any devices, in case the HDD may get into an even worse situation.

You may contact the manufacturer for repair, or other trusted company which provide data recovery service. The problem is unknown, the fix may be as simple as open the HDD case and reconnect the cable, or unfortunately the HDD was total lost.