I had Rocky Mountain Spotted tick fever and didn't ride at all for months.  I put a new battery on my Warrior and it still wouldn't crank.  The guy at the shop said the oil needed to warm and lubricate the clutch properly(sounds strange), because it had been sitting for so long.  After various attempts, the thing fired.  I rode out of the garage and up a hill to my house to grab some gear.  When I shut the engine off, even with the clutch disengaged, the starter motor was still spinning and the battery was sizzling.  The whole machine was creeping forward.  I had to disconnect the battery leads to stop the starter.  Now the thing won't start at all.  I have a new battery, can't find any damaged, grounded, or disconnected wiring or connectors and the fuse is good.  Does anyone have any advice, or is it possible that my atv has become home to poltergeists?  My local shop won't take it for at least three weeks because they are backed up.  

sounds like possibly the starter solenoid is bad.

the starter solenoid activates when you push the start button, and tells the starter to turn.

i would check it and also check the start button on the handlebars.  

Thanks for the advice, but I forgot to mention that I did install a new Yamaha solenoid.  Here is something else though:  I bought this atv used from a friend.  He was using a screwdriver to start it because he lost the key.  I put a new key switch on, but then lost my key so I plugged in the old switch until I can find my key.  Could this affect the starter?  Also, is there a way to check the button you push to start?  Like with a test light or something?  I really appreciate any advice.  I'm going stir crazy here and tromping through the woods in my snake boots isn't as much fun as riding through on my atv.  

yes if the switch has been damaged which can be by using a screwdriver to start it, it could cause issues with the start wanting to engage.

you can check the switch for continuity using a meter.
you'll have to follow your wiring diagram to proeprly test the wires.