Trek 7000 Mt. bike's crank will all of sudden start spinning free as I peddle. Seems to happen more in wet conditions.

What do you mean by seams to fire but won't Start ? When you turn the key to start what happens ? Does the starter spin the engine ? If so this would be a engine cranks , now if it does spin the engine an the engine doesn't start an run this is call an cranks no start condition .Now on the other hand if the starter doesn't spin the engine when you turn the key to start ,then this is referred to as a no crank - no start . There are very different diagnostic steps for each of these conditions . Your best bet is to have your vehicle diagnosed by a qualified technician .

If it was clicking the resistance motor is stuffed replace it they are quite cheap and easy done, but also make sure the flywheel is tight as they loosen over time as well. You'll need the crank tool, I made one from a m20 metric fine thread and drilled and tapped but you could probably get one from a local cycle shop. Easy job, worth doing these bikes are real nice ??

If the wheels spin free then I would look at the bottom bracket. All of the force you use for pedaling relies on the bearings in the bottom bracket being good. Are the pedals hard to turn by hand? Do the pedals themselves spin freely? If the wheels turn, this really only leaves these two rotating points as possible suspects.

Pedals are a thin 15 mm wrench, which is a specialized tool. Contact your local bike shop for assistance

It could be a hex nut or 9/16 ths bolt. Contact your local bike shop for asistance

Trek doesn't use a date code system. The headbadge (nameplate) can identify the year the bike was made by comparing it to pictures at TREK.com, under support

This bike had a square-taper bottom bracket. What happens with this type is that the bolts holding them on become slightly loose over time. The crank arm begins to wobble and the "wollows" out the inner hole on the crank arm such that a new one will have to be purchased. They are about $15.

The only parts envolved are the cranl arm and the both that holds it in place.

If this is a coaster brake bike (single speed, no hand brakes) then the problem might be inside the rear wheel hub. If that is the case then you can only fix it by completely dis-assembling the rear wheel hub - or it might be simply that the chain is slipping, which would not happen unless the chain is too loose which would be indicated by the bottom of the chain hanging down too low. However, if this is a multi-speed bike, then it could be that the chain and rear-wheel cogs are worn - which can be fixed by replacing the freewheel and the chain - however, it takes a lot of use or rust and dirt before that level of wear happens.

Tighten it, soon , before you do some damage to the interface and then it will never tighten fully.

Try this:

http://parktool.com/repair/byregion.asp?catid=59&imageField2.x=35&imageField2.y=18

This isn't Bike Repair 101-level stuff. Take it to a reputable bike shop and have them teach you while they do it. If they're cartridge bearings it's fairly simple. Next time, you can handle it. Be advised, crankset removal tools are specialized and expensive for the casual bike owner who would use them only once every few years..