iMessage log in Problem
This is a commmon problem with Hackintosh'ed computers. Is the computer you are using with OSX genuine?

Wether it is a real Mac device or not, the steps to fix this should be very similar. Here is a very long thread describing each step to fix this in great detail.

To start off, I would make sure that your Apple ID is verified. You can check the 'Verified' status of your AppleID by logging into AppleID's online management.