Sounds as though your laptop is not working with APM or maybe you just need to boot with the correct diver. Try this: Open a term, and enter sudo halt See if that kills the Xserver properly. Also try CTRL+ALT+BKSPC to kill the xserver. You can specify which driver to use at the boot prompt. I would suggest

boot: knoppix lang=us xmodule=ati

or

xmodule=vesa or xmodule=radeon