BleepingComputer.com: dvd rom

Software -- under what circumstances does this happen? Are you on the internet, is there a particular program running, does it happen at turn-on or if the unit has been running for a while, etc.

Hardware -- a common problem is a bad tray open/close push-button switch. The switch behind the front panel button is very cheap and prone to problems. The "springiness" to the action is provided by the same piece that closes the circuit. A partial collapse of the contact will cause the switch to intermittently short out, making it act like the button has been pressed. How does the button feel when you press it? There should be a slight-but-noticeable "snap" or "click" to the feel of it. These switches are cheap and relatively easy to replace. Sometimes, too the plastic button binds in the panel and never fully pops back out when pressed -- try wiggling it by probing its edge with a round toothpick to check this.