Game Crashes at Start-Up at the end of Mojang loading screen

Basically what my problem is that when i open the launcher i open the game and then the mojang screen starts to load up and when it gets to the end i lose connection to the monitor then it crashes sometimes the game just crashes or it restarts my whole pc. I did turn off my firewalls and it worked once but then while playing i turned it on and it crashed then i tried to run it again after turning off my firewall but it would crash it wouldnt even open up anymore