td4 abs light

hello. after years of wanting one i finally bought a 2001 3 door td4 which is in fantastic condition, problem is i brought car back from peterborough on thursday and it drove like a dream, everything working etc... now its been sat on drive for 2 days and when ive come to it today the abs warning light has come on and wont go off. also the door lock on the near side will lock fine with central locking but wont unlock. anyone got any ideas please ?

ive sorted the central locking problem (door lock from scrappy). when the car is started, the ABS light comes on, but you start driving and the light goes off. anybody know what this could be. p.s. when putting my sony headunit in, i accidently knocked the hill decent button, could this be anything to do with the light????

cheers, stu.