Check all your connections first. that's the simplest suggestion i can make to start... I would also check to make sure the red slide switch on the left bar is on and the keyswitch is on. then we will get into you quad in depth more.
Welcome to the forums.
Thanks for the quick respone, The previous owner said the problem started with it sputtering bad not reving up. Then it just stopped getting a spark. He took it the shop and they plugged up their machine to check for a code on the electical problem. The guy told him it wasn't the reverse rev limiter but it had an electical gremlin. They quoted him $200 to fix it. He bought a new 450 and parked the 300 in the garage for the past 2 yrs.
Like I said lets start simple..... on the right side of your engine (brakepedal side you will see a louvered cover Not the round one that's the oil filter but under the pedal remove it... you will see to sensors one is the neutral safety and the other is the Reverse lock-out switch. the rewind switch should have a single gray wire leading up and over to the other side of the quad... remove the seat and rear fenders it's easier to work on. ok now find that gray wire.. it should be plugged intoa holder with a gray and a gray/black. unplug the wire leading to the switch under the pedal. now take the harness side wires and plug them together with a short jumper wire you can strip the ends on a 3" piece of wire and stick it in the connectors if you want it will do for testing. now make sure you are in neutral and all switches are ON and see if it will start.
So I looked over all the connections and they look good. I found the sensors under the brake padel. I followed the gray wire to the other side of the bike to were it connected to a black connection that pulls apart . The other side of the connection is just a gray wire. I don't see a gray/black wire. it just connects to one gray wire then runs up towards the front of the bike. I noticed my neutral light does not come on ?? I pickedd up a new coil for $11 today .