2008 iMac stuck on blank screen when turned on.

Hi,

So my parents have this 2008 iMac, which they used a lot. The thing was sluggish , but got the job done. However recently the thing was going though some problems, the screen would randomly freeze, weird artifacts can be made out at random time's, and worst case; the screen turns white, blue, or completely glitches into this blobby mess of pixels simultaneously freezing the device. Generally in this case, I would reset the device (as in holding the power button until the system powers down), which generally fixes the issue.

However, just recently. The device did the same thing, glitches out and froze into a pixel mess. I did what was routine and held the power button, the computer shut off. But on rebooting; the device simply won't reboot. The screen stays blank, as the computer makes noises that sound like the system is going through some type of boot-loop. As of me, I went ahead and took it apart; and resorted to the LED indicators located toward the bottom of the board, watching the LED's; 1 and 2 turn on, as 3 would flash every 2 or 5 seconds. I thought it was the ram, as of that... I took out a stick of ram and booted the computer with one stick of memory.

At that point, the computer started up, and the chimes can be herd. Everything seems to sound routine, but the display yet is still not powering up, looking at the LED's, 1 and 2 were illuminated, but 3 isn't. Each time I click the power button, LED's 2 powers on (because LED 1 indicates power to the machine - LED 2 indicates communication to the board), the chimes sound, but LED 3 only flashes on and off, and stays off, with the display off. My observations indicate a graphics issue, but I'm kind of stuck at this part now. Any suggestions on how to fix this?

thanks!