Trying to think on why you having this issue
Just to clear it up some, I was helping him before and these were things we tried.
(1) Use a torrent (To make sure he has a good disk player)
(2) Use a different account (To make sure nothing on the account was keeping him from playing)
(3) Use a pre-completed game save (Because, we thought his game saves were getting corrupted)
There is probably more that I can't think of, but this is some of them.