I was loading up minecraft and every time I loaded up a single player world it crashed. When I joined a server, I couldnt join

i cant join servers and it crashes when i load a single player world.

*What I expected to happen was...:*I would play single player on a new world
Describe what you thought should happen here I though it would run fine.

*What actually happened was...:*It crashed when i tried to play single player and I couldnt join a server
Describe what happened here I could play minecraft at all

Steps to Reproduce:
1. load minecraft
2. play a single play world or join a server
3. get kicked from server or crash