One thing I did here was custom assign a particular rather loud wav file to the the "new device connected" and "device disconnected" items in the Control Panel>Sound>sounds tab there so I no longer have to looking at the screen when plugging or unplugging any usb drive or device.
Apparently the present installation is not detecting anything new like it should and may have been a bad install seen there. You can try running the "sfc /scannow" command at the Run command with the 7 dvd in the drive and see if that will help by replacing any system files if found damaged or missing as one idea.
Since you are seeing the other mass storage device present something is still working where this might be all that is needed if only one or two system files are involved. Or the one thing often overlooked is the regulation of the usb bus seen on different boards.
When going to take a usb flash for example from one system to another older case the drive will be sluggish and the owner complains of not being able to use some of the ports while having multiple devices plugged in or his own flash has to be plugged into a separate usb hub. Those are powered externally with an ac adapter.
You may have to consider that as a likely cause since you know all the drives work and the individual ports still work but not when having multiple drives plugged in suggesting the bus is being pulled down a bit. Some time back while in a Walmart I picked a small 4 port Cyberpower blue led hub that actually works llike a champ for any printer, external drive, enclosure, or flash drive plugged from simply providing an adequate level for each device.
Funny how we missed each other's own idea on using the system file checker on this!
But conisder the other on adding a good hub on to see if that will provided the power level correctly to see the drives and devices work for you.