Could it be a scratched or dirty disc?
Is "Unleashed" a single disc install or multiple discs?
I would venture to guess that it's a single disc, so maybe clean it (Water + soft cloth + stroke from center OUT, not in circles).
If the disc still looks bad, a cd scratch remover might be in order. I've never personally used one, but apparently it takes a small layer of plastic off the disc, eliminating or reducing scratches along the way.
If it's a mutli-disc install, maybe you missed a prompt to insert the second disc and it timed out?
Or maybe I'm totally off.
This is a legal copy of the game that you bought, right?
Because if it's downloaded or something this is a normal occurrence and it serves you right.
-rock