Tmobile my touch 3g (HTC Magic) doesn't give option to mount USB storage anymore

I have a Tmobile MyTouch 3g. When I connect it via usb to my 64 bit Windows 7 machine, I do not get any option to mount for USB storage as I typically have in the past. I also do not get any option when connected to my Windows XP work machine. I have tried getting the mytouch to dismount/mount the sd card under settings and then replugging in the phone with no effect. Not sure if there's anything else under settings I could try. When I look in Windows 7's device manager under USB there's an "Unknown Device" listed. I "uninstalled" this device by right clicking and saying "uninstall". Then I reattached the mytouch 3g and all I got was "unknown device" again. There appears to be a couple of forum posts on this issue, including here and here but none of them have been helpful. Only the last one seems to accurately 100% describe this problem, but nobody has responded to the post. How can I fix this? I'm hoping it doesn't involve resetting the phone to factory defaults.