Can I ruin a microwave oven if I use it with nothing inside?

If it turns on by itself, then yes, it very well might! Our microwave kept turning itself on for 7 minutes during the night. Luckily, someone would usually here it and unplug it. One time my friend warmed a roll in the microwave and left it. It set itself after that and caught on fire! Bye bye went the microwave because of it smoking me and my baby sister out of the house. Sorry I'm going rattling on!