Unity5: There is no dialogue box appearing when I press Save Scene As..

Guys can you please help me with my problem. I can’t start my thesis in school because I can’t save a scene. But, last week it’s ok. I don’t know whats the problem. I uninstalled it then install it back, but the problem is still there!

Also, when creating a new project, when specifying the folder directory, there should be a dialogue box, but the same problem arise. No dialogue.

I appreciate your help! Thanks!

Did you try pressing Ctrl+S ?