Are you worried because the MacBook Pro not booting from hard drive ? The operating system files that are responsible for running the machine is and providing a platform to running other applications. Its files are saved in the hard drive and if it is not booting then you should know there is something wrong with the drive. You need to fix the disk when the macbook pro not booting from hard drive. The disk utility present in the Mac can help you which can be run through boot menu. It may find the issue that is causing the problem but not necessarily be able to fix this so in that case you will have to format the drive. This deletes all the files from the disk including the operating system files. However when you resinstall the Mac OS X again the macbook pro not booting from hard drive problem get resolved. Then after you must be looking to recover the other data. You should use the time machine and see it helps and if it does not work the try the Mac data recovery software. You can make the recovery of all your files quite easily and quickly so get the software now and use it.