Minecraft launcher/minecraft crashing

I went onto my minecraft launcher and logged in then when I pressed play it went onto the white screen saying Mojang.It stayed on the screen for a few seconds then went back to the launcher saying that it had crashed and everytime I tried going onto minecraft it crashed.

Before that happened I was playing minecraft normally and I tried changing texture pack and it took a really long time so I exited then that was when the game started crashing.