iMac screen filled with lines and pixels: Please help

Hi all,

I'm a newbie here and quite newbie to Mac also. Got to know of this website from a goggle search. I hope anyone can kindly advise me of a problem with my iMac 27" (2009 model):

Upon bootup, I see some lines on my iMac screen.



It takes a lot longer than usual to come to the desktop screen.

When it does, there are many small square pixels filling up the desktop:



If I try to click on a program or file to open, the colour wheel will appear and spin forever. (The files and programs are all there.... just cannot open them.)

Does anyone know what is wrong with my Mac? I'm wondering if it's the graphics card.

I did an extended Apple Hardware Test during bootup and the result found nothing wrong at all!

Is there anything I can DIY or the only way is to send the whole iMac for servicing?

You advice and help is greatly appreciated. Thank u!

Thanks BlackZ.

The Apple Hardware Test did check the logic board and found no fault. Or maybe that test is not detailed enough to pick it up.

As it's no longer under warranty, Apple Service advised me to call any of their authorized service centres. Do you have any good one to recommend?

Just curious, did you have to pay for a replacement logic board? If so, how much was it?

I hope it doesn't cost too much for my iMac. Just the diagnosis of problem already costs $120 and transport I think close to $50.