Welcome to the forums. Double check that your battery cables are clean and tight. If that doesn't help, jump the two posts on top of the solenoid (relay) with an old screwdriver or something. This will bypass the internal workings of the solenoid and send power straight from the battery to the starter. If it starts, more than likely, the solenoid is bad. If it doesn't, test the starter.
To test the starter, get a set of jumper cables and hook one end to a known good battery. I like to use a battery in an automobile that I drive, so I know the battery is good and also it's a little easier to hook the cables. On the other end, hook the ground clamp to the starter casing or the engine. Firmly touch the positive clamp to the starter post. If the starter is good, it should turn the engine.
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.