would help if you posted back with full machine model # from ID plate so that we can know which type of PTO setup you have.... M/W, cuppla things to chk - If it's an elect PTO , there should be a short pigtail lead coming out of the PTO pulley assy that connects to the machine wiring harness close to the main frame. Make sure it is connected and has not been damaged. Visual chk with engine off.
With engine on and running at 2/3 + RPM's, measure voltage across battery terminals with VOM - s/b > 12.8VDC... if not, either you have marginal/weak battery or problems in charging system output. An energized elect PTO need on the order of 4 amps to remain energized - a battery going bad or an alternator sys crapping out will do it in.