2011 Hyundai Sonata battery 2months old. Car will not start. Thought I might have left the lights on, charged battery. Battery is fully charged, car will not start

When you say it will not start, that leaves all kinds of room for interpretation... Do you mean it will not crank or that it cranks but doesn't fire? Have you had the starter checked? How are the battery cables? Was it a cheap off-brand battery?

. Clean the battery terminals and cable connections with abrasive cloth. Clean the ground going to the frame of the car. Check the battery cables for hidden corrosion and breaks.

. Test all under hood and under dash fuses with a test light or multi-meter.

. Confirm that the starter motor cranks the engine.

Keep us posted with the results and we should be able to walk you through it.

Coworker had one do that... the Ignition switch went bad. But as TcGreaseMonkey and Odinn7 stated... there is a lot of possible reasons.