Hello John. I'm Greg, here to help you with this.
1) I'll give you all possible fixes for External Drive not detected in Windows 11:
https://www.thewindowsclub.com/external-hard-dr...
https://itechhacks.com/fix-external-hard-drive-...
https://www.donemax.com/data-recovery/fix-exter...
https://www.groovypost.com/howto/fix-usb-not-wo...
https://www.youtube.com/watch?v=-QxSdmnj9R8
2) Disable any 3rd party antivirus, or uninstall and turn on built-in Defender, to see if that resolves it.
3) Right click Start button to open Disk Management, scroll down to try to find the drive on the map by size and label, right click on it to assign a drive letter so it's detected in File Explorer.
4) Go into Device Manager to look for the drive under Disk Drives. It may be listed by it's model or Serial which you can google to determine which is it. Click on the Device, then Driver tab, choose Roll Back if available. If not then choose Uninstall, restart PC to reinstall driver. If that fails choose Update Driver, first Automatically, then if that fails choose Browse > Let Me Pick to try all previous drivers.
If no newer or this doesn't help, then go to the USB category in Device Manager, open each Enhanced, Hub and Host controller, from Driver tab select Roll back if available, or if not choose Uninstall.
If your keyboard and mouse are USB, first program the power button to effect the needed restart after Rolling back or uninstalling the driver. Go to Settings > System > Power & Sleep > Additional Power Settings > Choose what Power buttons do to choose Shutdown.
5) Test the drive using diagnostics to know for sure it's condition:
https://www.lifewire.com/free-hard-drive-testin...
Follow this up with a DIsk Check from the Command Prompt if necessary:
https://allthings.how/how-to-run-chkdsk-in-wind...
6) Check if the drive is detected in another PC. If so back up the data to a folder on it's desktop. Once you confirm all the data is off the external, wipe it with Diskpart Clean Command:
https://www.tenforums.com/tutorials/85819-erase...
If nothing else works see if you can run Data Recovery on it using
Recuva:
http://www.piriform.com/recuva/features
Then plug it back into the PC which cannot detect it, reformat in Disk Management:
http://www.wikihow.com/Format-an-External-Hard-...
Feel free to ask back any questions. Report back results for more steps if necessary.
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