Usually a slipping drive is something such as worn drive disc or a belt slipping as it is worn or needs a control adjustment, handles tightened etc. You may just need to pull the covers and see what's going on. Watch over things like springs and bearing wear whilst you are inside. Maybe the wheels turn while in the snow because the front moves easier in the snow- less friction on the skids. Official guess there... Let us know what you find. Here is a link that might be useful: Snapper parts

if tractor has gotten rained on, may be that park brake mechanism (located right on transaxle) may have rusted/frozen up. And, most all L&G tractors will not do well if left out in the weather - things like above and corrosion at electrical connections/switches happen quickly. They are not designed/mfg'd like an automobile.

***"What generally causes this type of failure?"*** The kind of "cascading" damages in a catastrophic failure like this engine suffered are typically due to a "set of circumstances" than from a "single cause" (I am referring to "dropping the exhaust valve") The valve seats are steel rings, pressed into a machined recess in the aluminum cylinder head. Under "normal operating conditions", the temperature of the engine remains below a critical threshold, and the valve seats stay in place. BUT, whenever "abnormal operating conditions" prevail, the temperature of the engine (especially the exhaust valve sector of the head) may go higher than the design temperature limit. If/when this happens, the exhaust valve seat loosens and jumps out of its recess. Once the seat is out of place, it prevents the exhaust valve from closing, and so the piston comes up and strikes the valve and seat. The impact may stop engine rotation instantly, or the engine may continue to rotate from flywheel inertia a few seconds as it spirals to a stop (the moment the exhaust valve seat came loose, combustion ceased). A "common cause" of overheating is when mice build nests, or caches of food, inside the sheet metal shrouds that duct cooling air from the flywheel fan over the engine cooling surfaces. An engine running with too little fuel in the mixture (lean burn) can also run hotter than normal, and that will eventually result in loosening of the exhaust valve seat, though that type of loosening may not always result in a sudden, catastrophic failure (but it can). Another way that exhaust valve seats can loosen (in an otherwise "normal" engine) is if valve adjustment is not maintained to the correct specifications. If the valves have too little clearance, the exhaust valve will "leak" a portion of the combustion gases past the valve seat during the part of the combustion process where it is supposed to be completely seated. Cooling of the valve seat and valve are primarily accomplished by having the valve and valve seat in contact with each other for the majority of the time that combustion takes place in the cylinder. This "closed time" allows heat to be conducted away from the valve and seat, into the cylinder head and valve stem, where the heat can then be carried away by both lube oil (inside the valve cover) , and cooling air from the fan. If the "closed time" is reduced because of insufficient valve clearance, the temperature of the valve and seat will increase higher than the design limit of the head, and the valve seat may loosen, or the valve and seat may be "flame cut" by the escaping gases. A good "forensic analysis" of the failed engine is needed to determine the reason for the overheating.

I think it might be that the connector to the horn has come off (this is not that unusual). If the interior lights are connected in series with the horn, they would go as well. The horn connector is found sometimes in the horn pad, or in the dash just under the instruments, or within the steering column cover.