Paypal button problem in Membership plugin

Something wasn't working with Paypal button in Membership plugin so I decide to remove it and replace it with a new Paypal button (this one : <form action="" method="post" target="_top">
<input type="hidden" name="cmd" value="_s-xclick">
<input type="hidden" name="hosted_button_id" value="QTN7XM8QUATFJ">
<input type="image" src="" border="0" name="submit" alt="PayPal - la solution de paiement en ligne la plus simple et la plus sécurisée !">
<img alt="" border="0" src="" width="1" height="1">
I tried to it but it don't working! The button is not appearing properly (just a question mark). I contact Paypal and they couldn't help (they don't help for with plugin button problems).

How can I find the original button that was in the membership plugin before I erase it? Or there is any other way to fix this?

Thank you for your help.


PS: Website: