I've had a few problems over the last 6 months where my macbook pro hangs on restart or I get a pinwheel when trying to open/run applications. The first time, I repaired the disk and disk permissions, and it worked fine for a few months. Another time it happened I had an "invalid sibling link" problem and googled some fsck commands in single-user mode to fix it - kind of worked. Ended up having to reinstall OS X not long after. Now I can barely open iTunes without it taking over a minute while a window says "checking itunes library" (my library if one an external drive), if I try to open any other applications I'll get the pinwheel and the computer becomes unresponsive. I've had to hold the power button down to restart if a few times. Once it was hanging on the grey apple screen and had to hold power button again. I'm backing up my home folder just in case. Anyone have input on why it's happening or what to do? Thank you.