problem with a check-out button

[Guest]

Hi,
I have a cart page where I show the selected products and the user must
click on a check-out button.
When the user clicks the check-out button the program have to hide the panel
with the selected products and show a panel with the "thanks for buying"
message (and save the data in the database).
The problem is that when the user clicks the check-out button for the first
time the program saves the data in the database but it doesn't hide the
panel with the selected products and it doesn't show the panel with the
"thanks for buying" message.
But when the user clicks the check-out button for the second time the
program saves the data again (now just save blanks records because the cart
was deleted) and now the panels works ok, it hides the panel with the
selected products and it shows the panel with the "thanks for buying"
message.
I don't why this happen.
Any help?
TIA
Regards,
Marcelo.