this is a machine that came to me for fixing so I have no idea what happend to it before I got it. I don't know what else I can tell you that is "useful" so elaborate please. I get the Apple logo and the spinning status ball- stalled at that. Just trying to verify that a wipe and reinstall is the way to go. Used Disk Warrior also plus Disk Utility from boot disk on damaged machine.
Maybe this will help:
Try setting up another admin user account to see if the same problem continues. If Back-to-My Mac is selected in System Preferences, the Guest account will not work.
If the problem is still there, try booting into the Safe Mode. Shut down the computer and then power it back up. Immediately after hearing the startup chime, hold down the shift key and continue to hold it until the grey Apple icon and a progress bar appear. The boot up is significantly slower than normal.