Right rear wheel seized up on Murray riding mower

I have an old Murray riding mower (model 38618x92e) and it wouldn't start the other day; won't turn over at all, no spark, nothing. I tested the battery, I put in a new spark plug, I changed the solenoid, and still nothing. This morning after I was finishing the solenoid, I noticed that the right rear wheel will not turn. I pushed the brake on & off a few times and nothing gives. Could something locked up here be the reason it won't start. And what causes the wheel to seize up? And advice would be appreciated. Thank you.