In that case, please start with this troubleshooting page here:
http://www.e-junkie.com/ej/trouble.paypal.order-not-processed.htm
Usually this problem will happen if PayPal is not sending us notifications of the payment at all, such as if you have your IPN settings disabled. The help page above goes over how to check that along with any other possible causes for the problem such as using PayPal buttons for your sales as opposed to our buttons.
If your IPNs are turned on and are showing as "sent" from PayPal's end please email us with the details of those IPNs so that we can investigate them further.
