Jammed starter - if the lights dimmed when you turned the key, it implies that the starter solenoid is operating and that the starter is drawing the current. Try sticking it in reverse, taking handbrake off and try to push it. This may free the starter, if not, try hitting the starte gently with a hammer or screwdriver. Starter may have "other" end exposed with a square or hex shaft projecting - try sticking a spanner on it and trying to move it. Let us know how you get on.