I am having a very similar problem. It does seem to be 'model' dependant. Some models (STL files) work, some cuse the lock-up. It doesn't seem to be dependant upon file size. Files that I opened and sliced OK in 14.03 now can be loaded.
When this happens (lock-up), this is what happens: The model seems to load OK, however I cant see it untill I click on the'View Mode' icon and then 'Normal' - it usually then 'shimmers' into existance. I can rotate it, zoom in and out but as soon as I select something in the 'View Mode' (eg. 'Layers') Cura locks up.