Usually, issues like this are caused when your web browser has cookies disabled. You'll need to make sure your browser is set to accept cookies so you can use SkyGeek.com without trouble.
Please change your browser settings to accept cookies and the shopping cart should work as expected. We also recommend that Java Script be enabled as well.
If the item is on clearance and the In Stock quantity is not visible, then the item has sold out and you will not be able to add it to your cart. You may be able to select to add the item to your cart, but it will not appear once you go to your cart. Typically, we will order more of a clearance item, and if we do, there is typically a price change. You can contact us at email@example.com to see if/when the item will be available. But, any status of availability other than In Stock (even if it is noted as On Order), may not be accurate.