@SpeedStep I'm now running with my other monitor which also acts as a powered hub. Connecting it to one of the Optiplex USB ports results in a Device not recognixed popup. Viewing Devices by connection in Device Manager shows a USB Root hub attached to the USB2 Enhanced Host Controller, with an Unknown Device attached to that Hub. There are no USB devices connected to the monitor's USB ports.
Plugging a USB sitck into one of the monitor's USB ports does nothing at all.
Disabling the USB2 Enhanced Controller results in the plugged in memory stick being recognized, with the popup 'This device can perform faster..'
Have you tested a usb mouse and keyboard in " either front or rear ports of this Optiplex"?
Yes, mouse & keyboard, and any other USB1 device, including an old USB1 CDR/W drive work fine in any port.
It is possible to corrupt the Registry for USB Mass storage in all versions of windows
specifically to prevent mass storage devices from mounting. There are also USB based Malware that get into the partition of the USB Device that cause the same issues.
