Connected positive to positive when trying to jump start another car?

Hi, I just did the cardinal sin of wrongly connecting my jump wires when using my Megan to start another car. There was a lot of sparks on the positive battery terminal, followed by the wipers coming on and all electrics jamming. I had an error message on the dash that read - Electric Fault. Having disconnected the battery to stop the engine, and then reconnecting, I now have no power at all. Does this mean the on-board computer has had it? and are there any checks that I can make to before handing it over to a garage??

Thanks for any help you can give.