iMac G5 display has gone all purple and weird!

Hi all. I'm a newbie, and I've joined Mac-Forums because my iMac G5 has suddenly developed a most strange display - horizontal lines and a general purple haze, particularly around the desktop icons. I've taken a couple of photos but I don't know how to upload them so you can see what I mean.
Anyone come across this before? Is it likely to be the graphics card or something more serious? This machine did have a new motherboard or logic board about 3 years ago (can't remember which, exactly).
Help!

Is this an iMac G5 iSight or the older ALS or even earlier iMac G5? If it's the iSight, I have one idea to try.

Thanks for replying...

It's the ALS - the last model before iSight came in.

I think the ALS has the same plug. Find where the LCD plugs into the Logic board. On the iSight it's a small plug with two tiny screws. If yours is that way, loosen the screws and pull the plug and plug it back in.

On my Sight the jack on the logic board was dirty and I used some contact cleaner and it never messed up again. Not sure if this is your issue but worth a check.

I just checked the service manual for the ALS and it does have that plug on the logic board where the cable from the LCD plugs in with two small screws holding the plug in the jack.

Thanks dtravis7 - I'll give it a whirl!

Tried that dtravis7 - no joy! All 3 diagnostic LEDs lit ok, tried disk utility as well with no luck. Looks like something more serious might be going on...strange, though, it was fine yesterday.

The plot thickens...when I change the display to 256 colours or thousands, the lines disappear. Except in the desktop icons when they become vertical white lines. Weirdly, whenever I open any application, the header bar goes purple but the main display is fine! ***?