P190s, no power?

I just had the same problem with a P190s monitor suddenly dying, and your solution worked - and then it didn't.  That is: I unplugged everything and held down the power button 15 seconds, plugged power in again, and the monitor came back to life!  And I plugged in the VGA cable, and the screen showed up just fine.

But then, just to be sure, I tried turning the monitor off (with the power button).  It wouldn't turn off!  I unplugged the VGA cable, and then the power button was able to turn it off.  But then, the monitor went dead again - I can't get it to turn on.  Even the 15-second trick doesn't work any more.

During its brief period of recovery, the monitor showed its usual perfect picture.  So I'm wondering: Could there be something wrong with the power switch itself?  If so, can that be fixed?

~ Thanks in advance

~ Ken