MY bike locks up in the winter all the time, if there was any snow on the ground last time you rode you've probably got ice in the shoes. What're the symptoms? If it goes in gear and revs when you push the throttle you've got an entirely different problem than if it goes into gear and stumbles when you push the throttle. If it wont move I'd suggest warming up the brakes and turning the wheel as hard as you possibly can, don't drive it to break them though or you can toss axles.
-2007 King Quad 450 (Work Horse)
-1984 Honda TRX200 (Donor)
-1989 Skidoo Mach 1 (Play Toy/Winter Headache)
-1966 Series IIA Land Rover (Major Project)