Q: I've installed OS X on my macbook pro... and then restarted it... but it's now been restarting for about 3 hours??  Help!!

Hold the power button down to force a power down. Then restart and immediately hold the option key down. If two hard drive icons appear select Macintosh HD and hit Return.

If only see Recovery, select it and hit Return. On the next screen select Disk Utility. In DU do this:

1. In the list at the left, select the your hard drive. (Be sure to select the item that’s indented to the right in the list, not an item at the far left.)
2. Click First Aid.
3. If Disk Utility tells you the disk is about to fail, back it up and replace it. You can’t repair it.
4. Click Repair Disk

After that is done restart as usual.