Hello, I've developed a sudden problem after booting up my Mac today. No core apps will open. This includes Mail, App Store, Terminal, iWork, iLife and anything else from Apple. Clicking on the dock icon causes it to bounce once or twice then revert back to staying still. I am on 10.9.1, using a Mid-2010 iMac 27". No problems are reported when verifying the disk under disk utility, and repairing permissions hasn't helped. Thanks for any help!