i think a good place to start would be telling people what hardware you are using... then searching the same hardware for issues here... or google "my hardware xwindows crash ubuntu" and see if that helps you resolve the issue ...same for the debian/ubuntu wireless network wizard thing.
you might also see some error logs the easy way by hitting CTL+ALT+BACKSPACE it should dump x and you should see some crash on the screen... but more then likely you just have some hardware incompatibility with the default configuration of x.conf etc.. which will need some research.


