(sorry;; I should have posted this on 'answer' but clicked a wrong one before)
미쳤어 = (someone is) crazy. you can say she/he is crazy '쟤 (진짜, 완전) 미쳤어" "저 사람 (진짜, 완전) 미쳤어" I think we often add the adverb '완전 or 진짜" (completely) 미치겠어 means " I'm going crazy" "I'm getting crazy" I think it's "wo quai yao feng le" in chinese. you use it when something is bothering you, or driving you crazy. '미쳐다" is a typo.. I think you wanted say "미쳤다" "미쳤다" and "미쳤어" are the same, but I think "미쳤어" is more colloquial. and when you want to say "are you crazy?" you should say "미쳤어?" not "미쳤다?"