iTunes app on iMac

iTunes won't open on my iMac, all of a sudden. The icon in the Dock keeps jumping up and down without opening. Had to Force Quit 3 times. Anyone know what I should do? What might be the problem? Thanks in advance!

What iMac? What version of OS X? What version of iTunes? When did it start doing this? What changed to cause this behavior? Have you closed all application, rebooted the Mac? Have you repaired permissions?

OS X Version 10.7.4 iMac 20/2GB. Trouble started today. Not aware of changes that caused behavior. Yes, closed all apps. Didn't reboot. Will try that. Not familiar with "repaired permission." Please advise. Thx.

Try the reboot first, and for repairing permissions: Disk Utility 12.x: Repair disk permissions

Rebooting worked. Will make note of Disk Utility for future reference. Many thanks for your prompt and helpful replies.