I suggest giving more information on the circumstances of the crash, posting a console log etc.
The topic title is a bit hard to understand. Does it crash when you switch to full screen. Does it crash when you try to join servers? Or does it only crash while you're in fullscreen trying to join a server?
Something like this is just so ambiguous.
"Hey I did a faceplant in the snow. Tell me how to not do that."
"Uuuuuuh."
