iMovie Update seems stuck

Hello, I started running the update through App Store and it is stuck since Saturday (its now Monday). It says it is at the point of 'running package scripts' I have tried cancelling it, force quit and restart my computer but nothing works to cancel it. I also get a message 'your computer can't be restarted now because software is being installed: iMovie is being installed. Interrupting the install may damage your computer. You can install when the install is complete'.

What should I do?