Instead of chaining up the box blade, get a Quick-Hitch. Then it's very easy to just drop any three point implement. You can often hook up without getting out of your seat. The loader is super easy to drop also.
Then you'll have freedom mowing.
To the OP, did you try wiggling the PTO lever? On mine that switch will get debris on it and not sense the OFF position. Just hold the starter switch and wiggle that lever to start it. Ditto for the treadle pedal.
Both these I fix by just blowing out that switch area.