If the problem coincided with hooking up the APC UPS that may indicate the problem is with the UPS.
Somewhat similar situation discussed in the following link:
http://www.velocityreviews.com/forums/t527369-apc-ups-usb-as-unknown-device.html
Your situations seems similar as from the "System Information" file the "problem device" has an Error Code "This device is working properly" yet remains an "Unknown Device".
I would suggest to detach the APC UPS from the computer and uninstall any related software.
Restart the computer and see if the "Unknown Device" problem resolves.