Grey screen with vertical lines

[Lizzy Borden]

Hello,
I have a 1 1/2 year old iMac. Lately I will be on the computer and the screen just turns to this grey screen with vertical lines. The only other thing that I have noticed is that my desk top pictures, a slide show, disappeared. The desktop just has the star burst picture. Also when I get the grey screen with lines, I can't use any keystrokes to shut down. I have heard this is the logic board. How can I test to see if that is the problem.
Thanks

 

[chas_m]

Your Mac came with Apple Hardware test on the restore DVD. Just insert the disc, restart the machine and hold the "D" key. Do the long test if you can spare the time (like overnight).