Once a day or so, my new HP24f external monitor turns all while, or green, or yellow, and the computer starts making a loud continuous sound and stops working. I then have to manually shut down the computer by pressing the power button. No pattern in when this happens. sometimes many programs open, sometimes now. sometimes early morning, sometimes end of day. monitor is new. computer is DELL XP15. I go to Windows Event Viewer but can't find any further information on the error. The only thing logged is "the system has reboted without cleaning shutting down first". There's nothing under "Hardware events"