Check programs like netlimiter and AVG and disable them if you have them. I noticed, when my dongle used to work, that netlimiter interferes with the com port a bit. Also after you uninstall try deleting the files that are left (like user data folder and settings folder or something like that) check device manager under ports tab and make sure huawei modem isn't still there. Then reinstall.
I ran into some install problems when it wasn't picking up the card because the modem was still installed so I couldn't reinstall
I ran into some install problems when it wasn't picking up the card because the modem was still installed so I couldn't reinstall