I have been using ver 4.0 for a couple of months now, probably weekly it fails to load, I have fixed this so I now use it every time, follow these steps .
1: start task manager and end any tasks called cura
2: go to installation directory ( usually c:\program files\ultimaker..
3: find cura.exe
4 right click on it and select properties
5: click compatibility mode and choose windows 7
6: click apply, leave this window open
7: run cura, it will be slow to run, when loaded close it down
8: go back to properties window , uncheck compatibility mode, click apply and close window.
9: run cura, it should load faster now, have fun, you may have to do this every now and again especially if you don’t use it for a week or two but it’s five minutes out of your life and it’s a fantastic program