When you boot up, right when GDM starts (when you can see the mouse), hit Ctrl+Alt+F1. This will drop you out of GDM and back to command line. Log in as root, and use your normal password. Once you are logged in, type in this command:
gconftool-2 --type string --set /desktop/gnome/session/required_components/windowmanager gnome-wm
And then after that, in case you have fusion-icon installed
apt-get purge fusion-icon
Once both of those commands have finished running, reboot. This will make the default window manager Metacity, and (in case you started Compiz the dirty way) prevent fusion-icon from overtaking it, so you should be able to boot as normal again. Go into CCSM, uncheck what you believe to be the culprit effects, then run this command in an open terminal:
gconftool-2 --type string --set /desktop/gnome/session/required_components/windowmanager compiz
This will change your startup window manager back to Compiz, and hopefully without the problematic effects it should boot fine.
the beauty of linux is that the rabbit hole goes as deep as you want it to go.