What is causing the cartridge carriage to be jammed?

The cartridge carriage is jammed, and will not move either with power on or off. There is a plastic cover that covers the cartridge's when they are in their "home" position. So I can't access the cartridges with power on or off. I would need a special star-shaped screw driver to remove the cover, in order to access the cartridges. Perhaps then it may reveal what is causing the cartridge holder to be jammed.