My staffie is 3 years old and this morning he keeps shaking, won't eat and won't go out for a pee, and can neither jump on the bed. What is wrong with him?

He's sick or injured, and that covers anything and everything! Not nearly enough to go on, so get him to a vet ASAP.

I'll second that, sounds like a reaction to pain or discomfort of some sort, a vet is your only option.