If you uninstall and reinstall you will not lose your Multiplayer info on either regular or extinction, I also believe you don't lose your saved Campaign data. I did it with my disc copy and it was still saved.
Also, after uninstall be sure to turn the system off and unplug it for 2 minutes, then plug back , then watch the power brick to turn orange, then turn on that will clear the cache.
I moved you to your own thread so that we can further assist you. Did you wait the full 30 seconds when you unplugged the power cord from the Xbox? Re-installing on a wired internet connection has also helped players experiencing this issue in the past as well.