error 21 and 13 can both be fixed a few short ways. Error 16 happened from not being plugged in for more then 5 hours or you erased your HDD when transfering your movie. It's your clock. Your clock is reset and it cannot read from memory what time it is on your stock, or modded dash.
It is a big drawn out process. If you don't know much about modding or working on xbox's, I suggest having someone else do it. It can be fixed though. It's not totally dead
*edit* Welcome to Se7enSins by the way
Have a look around. We have lots to offer here. We even have threads on how to fix this very problem. Enjoy your stay here. If you can't find it all, I'll help you out.