I'm trying to use Xcode but it always gets stuck on this loading screen (attached image). I've used it before (for about an hour) and it works but I can't seem to get it to work anymore. I tried reinstalling it (I didn't uninstall, but merely re-ran the installer), but to no avail. It's always in the same place and I'm running OS X Lion on a 2.5 year old macbook. Help please.