First check the battery, if there's no power, then you either got a dead battery or something that drained it (headlights? foglamps?). From there, it could be a dozen things that may have gone wrong, whether it be corroded wires, blown out fuses, burnt out alternator, etc. But if you got to work fine, and you found out it was dead 2 hours later, I think it'd be a drained battery. I've left my fog lights on several times and in 3-4 hours, my car wouldn't start either (the temperature outside wasn't too hot as well, ~80 degrees F). The only thing that'd remotely light up was my alarm LED, and even that was weak.