If your OS hangs on blue screen then adequate approach to be taken in order to resolve the same issue. Actually in some point of time Mac refuse to boot and later turns into blue screen while start-up which is quite awful situation. Isn't it!! The probable reason behind OS hangs on blue screen could be due to boot sector corruption, software conflicts or hardware related issue etc. Now come to fixing this problem because no body likes that their Mac failed to boot. So for fixing the problem first and foremost step you can take is to simply restart the system because generally minor start-up problem is resolved through system restart. Else you can repair OS hangs on blue screen issue through repairing disk permissions by using disk utility. Alternatively running FSCK command in single user mode would be the option for resolving this startup trouble. At the same time there might be severe data loss that can be fixed through utilizing data recovery. This can be done through either previous backup or by utilizing third party program. In unavailability of sufficient backup it is suggested to go with Mac Data Recovery Software that is one of the efficient and smart of getting lost Mac file back. Hopefully the above discussed information would be helpful in fixing OS hangs on blue screen issue.