Since yesterday my Viewsonic 22" monitor (VX2255wmb) keeps showing its on-screen menu incessantly, without my touching any of its buttons. The menu comes on in the centre of the screen, stays on for 8-10 seconds, disappears for a second or two, then repeats the cycle. This happens whenever there's a signal being sent to the monitor.

I can't actually navigate the menu when it appears on-screen. Pressing the power button, or the Up and Down buttons on its right edge dismiss the menu, only for it to reappear again.

These symptoms have appeared before, but earlier they'd stop after 5-10 mins. The power button on the monitor has always been iffy, but now it doesn't seem to be working at all--have to switch off power supply from mains when I leave my desk.

Using DVI input on this monitor as my HP desktop has DVI output.