We have a Murray Lawn Tractor, model # 42576X92B, which was overhauled last spring, it was running fine when stored for the summer, now it will not turn over, replaced the battery, and it still will not even attempt to turn over.. turn the key, nothing...

This link is isn't the same model but maybe something's you haven't considered.
My 1782 won't crank using the key - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information