Unity crashes importing 3d assets

As the title suggests I am currently having issues importing assets into my Unity project. I am running Windows 7 x64 the latest build of Unity (4.3). The problem is I now have about 20 models in my game, as it refreshes these items when you open Unity it crashes for no reason and I’m unable to open the project. It crashes on different items each time and even when adding the items initially Unity would sometimes crash. I don’t really know how to fix this. I tried opening another project and turning Refresh off. This has allowed me to open the editor but it breaks all of my prefabs because the assets aren’t being imported.

Any ideas on what I can try?

Oh I also think 99% of them are .ma files from MAYA.

Turns out the Maya files were being produced in Maya 2014 and I was using Maya 2012 still so Maya was crashing behind the scenes and causing Unity to crash as well.