Windows 7 only recognizes 4 primary partitions on a drive. If you have more and none are logical, then it will cause problems.
Edit: I should be more clear. You can have 4 primary partitions, or 3 primary and 1 extended. Inside the extended you can have multiple logical partitions. If you have 5, then only 3 could be primary and the other 2 would have to be logical. Does your drive setup fit these parameters?