Please follow the steps below to troubleshoot the reason that causes this issue:
1. For your reference, the scanning would take around 5-10 minutes for a 500 GB healthy hard drive in general conditions, but it would depend on how much space have been used of the disk. If your scanning time is within this time range, please wait patiently and do not stop the scan in the middle of the process.
2. For some reasons, the hard drive is disconnected from the computer, especially for external ones. To fix this issue, please change a new cable to do the recovery again.
3. Your hard drive contains a serious physical error (such as bad sectors, bad tracks). Please use a professional tool such as HDTune to diagnose your hard drive. If the diagnosis shows physical error, you may need assistance from a local data recovery lab.