Unity import assets crash

I started a project in Unity 5.0.1 and a few days ago I updated the project to 5.1.1, no problems with that. Then, I wanted to import the "The Blacksmith: Atmospheric Scattering" asset from the Asset Store and while it was importing, my Unity crashed. When I tried to open Unity again, it started to reimport all the assets, but after some time, it always crashes. Now I can't open that project. When I try to open the project in Unity 5.1, I get an error "Out of memory" or something like that and the only option is to hit "Quit". After a few tries, I tried openning the project in Unity 5.0, but it still crashes, I don't get the "Out of memory" error, it just crashes.

I hope you can help me with this. Thank you.