Help!! 2006 Polaris sportsman 500

Hey I just bought an atv that has been sitting for 3 years outside. It’s a 2006 Polaris sportsman 500efi. I put a new starter on it replaced the spark plug. It started up great for a week. I left it outside for a couple of nights now it barely starts and when it does you rev it up and it will just die. Any help would be appreciated thanks.