Do you get anything on the console at all? It might be worth leaving it on a text virtual console (rather than X) overnight, and if it's hung, then try and issue a few "Magic SysRq" combinations to see just how hard it's hung. You might need to enable these first, not sure if Debian and friends enable it by default - "sysctl -w kernel.sysrq=1" should do it.
To issue the keystrokes, hit "Alt-SysRq-<letter>" where the most important ones are as follows:
