Possibly your carb float stuck and it leaked into the cylinder and now it is hydraulic locked..... Remove your spark plug and see if the engine will turn over. Make sure that the plug wire is positioned as far away from the plug hole as possible. Don't want a fire...
If there is gas in there then your crank case might have gas in it too... Quite common.
Most of us turn the gas petcock off when the bike is not in use.