firstly, if your saying that you downloaded from RIM an OS 5, its impossible, it hasnt been released yet.
Second, you can download the OS originally on your device (or rather a correct, latest released WORKING OS) from the stickied thread in the Tour forum.
Its easy to see.
"That's it then. Cancel the kitchen scraps for lepers and orphans, no more merciful beheadings... and call off Christmas."