iPod not syncing since installing Windows 8.1

I've just installed Windows 8.1 (jumping up from Windows 7) on my PC. Installed iTunes, then plugged in my iPod. Sync never even started up, though iTunes did open when I plugged in the iPod. I checked under Devices and Printers and I see that there seem to be two instances of an iPod there - one under Devices, and one under Unspecified. When I unplug my iPod from the PC, the first instance disappears but the instance under Unspecified remains (it's called Apple Mobile Device USB Driver). The first instance, under Devices, calls itself "Apple iPod USB Device" and it returns when I plug the iPod back in, so that's the instance that seems to be associated with the actual iPod.

Apple iPod USB Device has a yellow exclamation point next to it, and when I check under Properties for it and and then check for Properties under the Hardware tab I see a "Windows is uninstalling this device (code 21) message. This message never goes away, and Windows never actually uninstalls it. I can choose uninstall, and have done so, but when I plug in my iPod again, all this simply comes back.

At one point earlier today, iTunes began to "sync," but what it was syncing to I have no idea, because the iPod remained exactly as it has been - no new songs, no message in its little window saying it was syncing or anything. The "sync" lasted quite a while, and then when it finally finished, absolutely nothing had changed in the iPod.

So, even though plugging in the iPod starts up iTunes, they're just not seeing/talking to each other.

I've run the iTunes diagnostic, and it says it finds the iPod, but it also says (with a green light next to it) no usb ports found and (with a green light next to it) no firewire (IEEE 1394) ports found. It says All Tests Passed.