Ok, I'm at a loss. I tried installing a PCIe USB3 card, but it simply won't install. It appears that Windows will no longer install drivers for ANY new devices.

In fact, here's some more weirdness for you: the computer has a wireless keyboard and mouse. If I remove the receiver for those to another USB port, device manager complains that it can't find/install the drivers for new device. If I merely move the receiver back to the original port it was installed on, it works just fine. So the devices that were already installed will continue to work on their original ports, but no new devices can be added in any way.

I found some instructions on moving some of the USBstor files, but that doesn't seem to have done anything.

Any ideas? I've attached to images of how the new USB card appears in device manager.