iMac 17" display - thin blue line

I have a G5 iMac with a 17" screen.  Two days ago, a thin (1-2 pixels
wide) vertical blue line started displaying.  This line goes from the
very top to the bottom of the screen,  and it displays no matter what
application I have running. I have the screensaver set to ask for a
password, and the blue line displays there also. 

I've rebooted a few tmes, changed the resolution and color settings,
but none of this makes any difference.

Is there any way to get rid of this blue line?  Any ideas?

Thanks, Frank