To be serious, I also had this problem. When it finally stopped opening during boot-up (of it's own accord) the DVD drawer would then sometimes open of it's own accord while doing something, then it started doing it when I wasn't using the PC. If I went to push it shut it would see me coming and close itself. I AM NOT JOKING. I never found out why and the problem went away when I got rid of it all and built a new PC.
So I don't know why, but you are not alone !