Deranged (8)
(Other definitions for demented that I've seen before include "Nutty" , "Out of one's mind" , "Wild, irrational" , "Deranged, crazy" , "Crazy, insane" .)
'deranged' is the definition.
('unhinge' can be a synonym of 'derange')
This is the entire clue.
(Other definitions for unhinged that I've seen before include "Wild" , "Bats" , "Door may be" , "not flapping?" , "Mentally unbalanced like loose door?" .)