My imac was freezing when i would try to select any program. i tried restarting it and the same thign happened. i decided to just reformat everything and reinstall os x. i place the dvds in the drive and the first dvd runs fine. when i am prompted to enter the second dvd it freezes. i am unable to boot up anything. i have tried this 3 times and the same problem occurs could it be the hard drive or is it something else?