unable

(usually followed by `to'') not having the necessary means or skill or know-how; "unable to get to town without a car"; "unable to obtain funds"

(usually followed by `to'') lacking necessary physical or mental ability; "dyslexics are unable to learn to read adequately"; "the sun was unable to melt enough snow"

lacking in power or forcefulness; "an ineffectual ruler"; "like an unable phoenix in hot ashes"