WordNet sense 1 (informal or slang terms for mentally irregular):

balmy, batty, bonkers, buggy, cracked, crackers, daft, dotty, fruity, kooky, loco, loony, loopy, nuts, nutty, wacky, barmy, kookie, whacky, around the bend, bats, round the bend

WordNet sense 2 (afflicted with or characteristic of mental derangement):

insane

WordNet sense 3 (not functioning properly):

amiss, awry, wrong

WordNet sense 4 (not performing or able to perform its regular function):

nonfunctional, malfunctioning