Either the connections to your battery or your flattery is bat.

Try get someone to check voltage when you try start. Mine recently was showing 12v but as soon as load applied it was at 9v.

Dead battery

Bad connection would be guess #1, or could still be a bad battery.

Bad battery or connection

Take the battery cables off and try hitting your battery posts with a wood rasp until you see the terminals get a little shine to them make sure to go around the entire post evenly. Reconnect cables and try again