I attempted to install 10.10.1, upgrading from 10.10. Once I restarted the installation hangs and the boot screen sticks with the Apple and the status bar about 1/4 of the way filled in. I've let the system sit like this for at least 15 minutes with no progress. Any suggestions as to how I can in-stick it? It's a late-2011 MBP i7 with 16gb and an SSD.