UE4 won't launch my game (It either freezes, or says 'Launch Cancelled!'), then nothing else

So I’ve been trying to use UE4 for a massive project with me and a friend of mine, but everytime I go to launch my game, it either freezes and won’t do anything until I restart the entire program, or if i enable ‘cooking on the fly’ it shows me a console, then closes it with a message in the corner reading ‘Launch Cancelled!’. What do I do about this?