Previous Instance of driver still in memory--Ext hard drive

This is on a Toshiba external usb hard drive connected to a XPS8700 w 8.1 that works fine on other computers. The error message--cannot load driver...previous instance of device driver still in memory. I have uninstalled the ext drive from devices and printers where it appears with exclamation mark and error message, rebooted, removed and reconnected to diff usb ports, changed electrical outlets, checked Disk Management--doesn't appear there or in Device Mgr. Nothing works. Yet testing it on my other win 8.1 computer recognizes it immediately and I have access to all files.  It scans the drive and finds no errors. Files can be moved to the other computer's hard drive. The ext drive has been working OK on the 8700 for over a year. 

edit-- found the reason--USB Mass Storage Device has the error--previous instance.... still in memory. Any suggestions? Uninstalling and rebooting doesn't help. Preboot diagnostics were all fine.