HELP! My dog isn't using his leg, it just hangs there? what could of happened, and what can i do?

Ok, so my 6 yr old Rottiweiler is now limping, and can't put any weight on his leg, i asked him to lay down and let me examine it, because i plan to become a vet, and know how to diagnose a fracture or sprain, and with manipulation of his leg, i have deducted it is dislocated from the socket, but his leg had swelled to double the size than that same morning, so i felt lightly along the leg, and he whimpered when i reached the femur. Could he possibly of broken it?
My dad has a slightly large yard, and a old car he uses for parts. but it has never troubled him before. What could be wrong with him?

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