http://www.searspartsdirect.com/partsdirect/getSubComp.pd?modelNumber=917273404&productCategoryId=1509200&brandId=0247&brandDescription=CRAFTSMAN&modelName=LAWN-TRACTOR&diagramPageId=00001&componentDescription=PEERLESS%20TRANSAXLE%20-%202000-006A&documentId=P0107012&blt=06 If that picture comes up, you'll see the gears in your transmission. You'll see that some of the gears meet at a 90 degree angle. That's probably where your problem is; they are no longer meeting. You can probably repair these yourself, but it's time consuming.

According to the parts list, the engine has 2 "modules" aka coils. Apparently the kill wire to one has been disconnected??

Well thanks jim98520, I've been "around the block" a few times (mechanically speaking). I've had "good mentors" (mostly because I sought them out) all my life. But I am not the most important member on this forum, there are many who have spent a lot more working hours in the OPE field than I have. I have posted some incorrect info on this forum myself (sorry about your yard), but USUALLY, the more knowledgeable, experienced members stand me up straight, and I promise not to do it again. I do this because of people like my sister, and some aunts and cousins. People who want to try saving some money by DIY. People who want to have a second or third (or more) opinion about their "ailing tractorwhatever". People who have been ripped off (or think they might have been). This forum gives folks a means of getting info and opinions that they could not purchase for any price (haha, I visited a "website" once that "was charging" for answers! Yuk, yuk....YUCK!) Sorry about whatever circumstances have led to your "censorship" (if that be it). It "chillingly" reminded me of getting "chastised" (along with one of my bosses) at work. I sent an "innocent e-mail" to "a vendor" that contracts with my employer. Well, the contact person at the "vendor" forwarded my request for technical data to his boss who forwarded it to my "boss's boss's boss". Of course, all that trickled back down and first thing I know is my boss's boss is ticked at my boss. My boss (though he knew in advance about my intent) said "I guess we better not do that anymore." I said, "I bet your right about that." You might have to come up with a "different psuedonym" (psst. don't tell anybody at work about it).

It would be helpful if you would post the actual engine Model number and Type number found on the engine itself. But yes, your next step should be to remove the spark plug and check for the presence of compression on the non working cylinder. It is simple enough and effective enough to just place a thumb over the spark plug hole and see if it has enough compression to force past your thumb and escape when you operate the starter. Be sure you move the spark plug cable far enough away that you don't inadvertently check for spark as well (shocking). If you find that the cylinder has no compression, your next step after that will be to remove the valve cover from that cylinder and look for a pushrod to have fallen out of place. I think that is enough for you to work with for now. Report back as soon as you know something.