I am having issues with my computer going into sleep mode?

I have an HP Pavillion desktop, Windows 7. It has always just drifted peacefully to sleep after 30 minutes (I pre-set it there). Today however when I put it into sleep it started flashing screens black, white, red, yellow, blue, gree, etc, while displaying the words "Turn power:OFF" "Turn Power:OFF". I hate it and I want my computer back. What's wrong with it??