While overfilling isn't a good thing - I doubt this is the root-cause of your no-start problem, unless he overfilled it by CONSIDERABLY more than a measly 1/2-quart.
You say it gets spark - I take it you've confirmed this by pulling a plug and grounding it against the engine while cranking, yes?
Is it getting FUEL? Have you checked that the Fuel Pump is pumping and the Injectors are injecting?
Are the plugs wet? With what? Oil? Gas?
Do you have a shop manual? It's worth its weight in Iridium when you need it.
Fuel, Compression, Timing, Spark - these are the things you need in-order for the engine to run.
A bit more info for further diagnosis, please.