I recently moved and had the bike packed up in a crate for about two months. I threw on a brand new battery, cause I knew the old one had seen it's last day. Oil and gas is full, tank is on, spark plug is firing, but the darn thing won't turn over. It is making a horrible whining/screaching sound that the folks two blocks down the road can hear. It is doing this the entire time the engine is cranking. The noise is nonexistant when pull starting it, but either way it won't turn over. Any ideas?

 

If nothing was wrong when you packed it away in that crate, I doubt their is much wrong with it now. I would, drain the gas out of the tank and carb and check the air filter. The gas might just be to old and you may have picked up a "critter" that choose to make your quad a home.
Look for the simple stuff first.