Build EXE - Crashes

Hi, Im having a very serious problem.

I'm working on a game since about a year ago. I started it in Unity 4, and then I migrated it to Unity 5.0. Some things had broken because of the migration, but I managed to fix them all. Until there everything was ok. The problem I started having some days ago is that when I build the exe file, and I open it, and start playing, at some random times it just crashes and closes, and open the typical window says it has stopped working. You never know when it will crash, but eventually it will. I know this is not a problem of my computer, because I've been testing it in several computers, and it's the same in all of them. I also tried building the exe with script debugging, so It logs me out what's happening, but it's not much usefull. It just shows that everything's ok until it prints out "Crash!!!", but it doesn't say what caused the crash.

Please, any help??? This is an important work for education in schools, I need to solve it. Thank you in advance!