im having a problem with my minecraft 1.6.2 version and its really annoying me each time i log into a server and chat with other players in the chat it crashes my minecraft and restarts all over again

Put the summary of the bug you're having here

What I expected to happen was...:
to talk to other players in servers

What actually happened was...:
my minecraft crashed and my computer restarted

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...