I would try to uninstall 4.0, then maybe uninstall 3.0. Reboot machine. Play for a day, reboot again. Then install 4.0. If you still can't get 4.0 to run then google curse client or check if they have forums. I am pretty sure they have a help section, either in forums, or as a FAQ. In other words, aim to get 4.0 to work more than fight to get 3.0 to work.