Last time that happened to me (without the help of the cat) I started up again, but in safe mode - to do which you push the switch on button, and then keep on clicking on F8 on the keyboard and when it asks you if you want to start up in safe Mode tell it you do by clicking 3 on the keyboard.

Then when it started up it did it with everything in the right place, and I promptly shut it down again and started the normal way.