Take it back for either a replacement or refund.
If you bought it from eBay, you did NOT buy a new MacBook Air...
If it doesn't work, then return it to the seller. You will not be able to exchange it for another directly from Apple.
IF it is under warranty, then make an appointment at the genius bar of your local Apple Store and have it checked. It should be repaired at no charge if it's covered and hasn't been tampered with or physically damaged.
Question: i bought my macbook air brand new and it doesn’t turn on