umm, thats odd I have not seen this issue before... you could try opening up one of the other displays...
to change the display press ctrl + alt and the function key, they work as F1 = display... etc. Now login on one of the non-graphical displays (same login as the graphic one, note your graphical display is probably number 7) and then type HALT and that should do it. I'm not sure why it is hanging, maybe see if you can do the restart... it could be a task hanging. If when you are shutting down it asks you to display verbose mode, do that - you should be able to see where it is having a problem.. maybe we can then fix it. What version of Ubuntu are you using (i.e. Edgy / Dapper)?
Hope this is of use.