After Apple's 10 or so suggestions, including complicated mscongif and regedit approachs, all failed... I found this, easy enough to follow solution that actually worked. in a single user's post in the forums here somewhere. Can't find it again to say thanks to whoever it was, which prompted me to post it everywhere so everyone else can find it:
(Note: this is for Windows 8, but the solution for other versions is similar - you might need to try a few other folders, but are still looking for "Apple Device" under "Device Manager".)
- Connect your iPad/iPhone/iPod to your PC
- Go to: Control Panel > Device Manager
- Click on: Portable Devices
- Right click on: Apple iPad/iPhone/iPod > Update Driver Software
- Choose: Browse my computer for driver software.
- Go to: C:\Program Files\Common Files\Apple\Mobile Device Support\Drivers
Click okay and everything should suddenly work fine again. (I can't remember if I had to choose "trust" again, but if I did, I only had to do it the once and everything was fixed after that).