What happens when you take off the display command; do the sprites show up?
Maybe there is a glitch with the VSync parameter due to the graphics card you have who knows.
If they are still invisible, anything in the world could be happing in your source code causing them to hide. Providing the correct camera is active, and you are calling the sync command, and your sprite images actually exist, and the images are valid then only god knows what is wrong with your source code right now.
Why is there a Show Window command; isn't the window already visible anyway?