My monitor keeps flashing colors. It's stuck in this mode and I can't get into the menu on the monitor.?

Someone was playing around with it and now I've got their mess to clean up - as usual. It's a friend's computer monitor and yes, I've tried to look up this monitor on the Internet for it's manual or any help but the manufacturer doesn't seem to think that it's important and of course, no one can email them for answers. I can't remember the stupid name it's "Aopen" I think.