How To Fix A Ps 4 External Hard Drive. Click on the external hard drive connected and check its condition. This may help in this situation.
Check your drive is enabled and allocated — Windows. Connect the external hard drive with your PC. Try using a different USB cable if you have one.
Once Safe Mode loads, select Rebuild Database and press X on the controller.
Try to see if this works, and if it doesn't, continue for the next solution.
You may see a sticker covering the HDD bay cover. Make sure you reconnect it securely. Connect your controller via a USB cable and press the PS button.