Password Invalid wifi connection issues

my Macbook pro (late 2011 13" Mac OS X Lion 10.7.5) will not connect to my home wi-fi, it keeps saying 'invalid password' despite PW being correct, occasionally it connects, but I can find no pattern or reason for this inconsistency. my i-phone/i-pad are connecting fine and my housemate computers are also connecting fine. any help would be greatly appreciated.