Cannot get onto server and single player

When I try to go on a server, What happens is it says I cant connect to server when I have perfect internet and when I try to go on it says java.lang.NullPointerExeption: Group. Also When I try to go on a single player server it turns of the game and sends me to the launcher. I really need to go on a multiplayer server so please can you reply back asap.

Thanks
Nicole
Aka MysticalCupCake9