I´m having the same problem here: i ran combofix to get rid of a stickdrive "autorun.inf and recycler" virus. It worked, but i got rid of U3 also!
I´ve found this:
but i can´t try it here cause i have no admin privilege to change registry.
previously i´ve used combofix with another computer, witch resulted in autorun disabling but no effect on u3 sistem. I don´t understand why in some cases it "brakes" U3... May be combofix´s version.
There is another hope of solving this: uninstall the usb stickdrive and reinstall it. To do this i suppose one have to go into device manager and find the usb stickdrive and the option to unistall it. But, once again, i can´t try it here because i have no admin privileges. Can someone try it?