@mattk ,Matt, Something as simple as a low battery/bad connection or not charging could cause this. Possibly bad seat/reversing safety switch, faulty/loose wire/plug to clutch/PTO/switch, clutch faulty. Trouble shooting/parts/manual links below may help. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.
http://www.mytractorforum.com/forum.php
http://agriquip.co.nz/uploaded_files/Kingcat%20Manuals/Warner%20Clutch%20Adjustment.pdf
http://www.searspartsdirect.com/model-number/ZTS7500/0247/1506000.html?searchType=modelSearch&q=ZTS%207500&searchTerm=ZTS%207500
http://www.searspartsdirect.com/partsdirect/user-manuals/zts7500-craftsman-parts-rear+engine+mower-manual?manualIndex=0