Paypal Checkout Problem in Magento website

I m experiencing problems in paypal checkout in my magento website. When customers pay by paypal it only shows them transaction number not order number and most of the paypal payments are not completed it goes on pending payments. Whereas payments paid by card don't go on pending payments so i suspect there is some problem regarding paypal checkout. Contact me as soon as possible to start. Only contact me if you are experienced in magento and you are sure you can resolve this issue.