How can I empty my sony memory stick pro duo?

I can no longer take pictures w/my camera b/c my memory stick is full. I have deleted the pictures on the camera. After I have connected my camera to the computer, I have emptied the same pictures in the trash. I thought I erased the pictures in order to clear up space, but it is still telling me that there is no more memory space in memory stick. What do i do next? I have a sony cybershot camera, w/ a sony memory stick pro duo 512 mb.

thanks in advance