A few games have a freeze issue..lego star wars for instance.
Some games, GTA's ect must have the time set, the default 6th of june 00.00 of dashes will not do, the time chip in the xbox must be set, note the time chip will lose it's setting after @4 hours without power.
It could also be the cache files are corrupt, find and delete the e:\cache folder, it will be recreated automatically when a game needs it, and also delete anything on x: y: z: drives.