Can't open settings

Not sure, could be theme or another plugin, however it sounds like you may be running Multisite. It will not work currently on Multisite, there is too much undocumented crap for me to go that route, and quite frankly, multisite is a bad idea to begin with running all sites off 1 database and one server, wordpress is already slow to begin with. But from what you described it sounds like you may be on a multisite server. If yes or no please let me know and I can help you further if need be.