I agree, get a good battery and make sure all the battery cable connections are clean and tight. Then, if it still won't start, jump the two posts on the solenoid and see if it will start. If it starts then, your solenoid is likely bad. Note that a bad solenoid won't cause the engine to stall, but it can keep it from starting back.
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.