Pressing Ctrl+Alt+F1 will switch you to a console. (F1, F3-F12 are console screens)
Login as root, then enter the following to disable X:
scologin disable
The X will no longer attempt to start.
'scologin stop' will just kill it until you change it or reboot.
You may need to configure the video card, monitor, mouse, or all three before the X will work properly.