I just purchased a Samsung S27C39 curved computer monitor.  Upon powering up, it is stuck in what looks like a test mode, cycling through full screen color Red, Green, Blue, White, Black with about a second on each.  Happens with or without an HDMI connection to a laptop.  Tried disconnecting monitor power for a long time and then applying power, disconnecting power with long push (30 seconds) on the power/control button then applying power, and applying power and then long push on the control button.  None of these actions change the situation.  I cannot get to the monitor menu.  Connecting to a laptop via HDMI does nothing.  I had been using a smaller flat screen monitor with the same laptop with no issues.

Need some hints on how to get the monitor out of test mode.