If you get the description of the button when you move the mouse cursor over it, that should be close enough. Once you click the button in the correct order, the door should unlock and open (giving you a bit of experience for solving the merchant's riddle).
Have you talked to the merchant about this? Try talking to him again, and see if that helps with the buttons.
Are you sure you have the correct order (far right, middle right, far left, middle left)? Try a different order, and then the correct one again.
If all else fails you should be able to bypass the door using the procedure in the
armory trick in act 1 topic (and repeat it to get out), but you will miss the experience and completed quest.
