I also have a Pre3 and experienced the same problem. After connecting as USB device and disconnecting via "Eject", the photo app and the internal music player spin endlessly.
Formerly I also did a reboot, which fixed it, but was inconvenient.
Yesterday I may accidentally have found a workaround:
1. connect via USB
3. while the USB cable is still connected, try the photo-app
4. if the spinning wheel is shown, reconnect as USB drive
5. eject again
6. open the photo app again. This time it opens and no spinning wheel is shown.
I only tested that twice now, but both time it worked and I really hope, that it works every time and not only for me.
I'm on windows 7 home premium 32-bit and have a German Pre3
P.S.: Every time I connect, win7 asks me to scan and fix my Pre - what will happen if I select to do this?