Time Machine Unresponsive

1 - switch off time machine - you should be able to at least switch off time machine in system prefs if not...

2 - unplug or do whatever it takes to make the desintation drive for time machine un-available (ie turn off your Time Capsule, unplug your usb or firewire drive you were backing up to)

3 - try to switch off time machine again

assuming 1-3 above worked, with time machine still OFF, you should be able to get to time machine in system preferences. verify this works. before going on.

now you should be able to plug in the drive you were once using for time machine and be sure to answer NO on any dialogs that pop up asking you if you want to use the volume for time machine or you run the risk of being back at step 1 with unresponsive system preferences.

rename the sparsebundle file you were using for time machine. it'll be called yourmacname.sparsebundle. rename it to yourmacname.sparsebundle.NOT. If there is enough room on the volume to create a whole new backup, you should be able to turn time machine back on and make changes to things. If there isn't enough room you have something to think about. Do you want to delete the sparsebundle and start over? You will be doing without a backup until the new backup completes (which can take many hours starting from scratch).

Bottom line: You shouldn't depend on time machine as your one and only backup solution! Either do TM backups to more than one destination (by using TM prefs pane to switch to a different disk), or add another backup strategy such as CarbonCopyCloner, dropbox, mobileme, crashplan, manual copying to a network drive, etc, etc.

hope this helps...