无法 (wú fǎ) means 'unable to' and stresses that there is no method or way, so the action is impossible. Compare with 难以 (nán yǐ) 'hard to', which implies difficulty but not impossibility. In conversation, 没法儿 (méi fǎr) is the casual version of 无法; 无能 (wú néng) and 无力 (wú lì) instead describe personal lack of ability or power.