account admin availability cart control date define entire inactive inventory limited limited-time ordering preferences prevent products purchase sell seller selling setting stock turn unavailable

When I sell out, is there a way to turn off the cart to prevent ordering?

You may just want to use Inventory Control for products that have limited stock or limited-time availability:
http://www.e-junkie.com/ej/help.inventory.htm

That said, you can also make your entire account inactive for selling until some future date, which you can define in your Seller Admin > Account Preferences > "Make all products 'unavailable' for purchase till:" setting.