I hope someone might be able to provide advice on a problem I am having.

I have a 2008 Imac running Mavericks.

Everything was running smoothly this afternoon. I stepped away for about 30 minutes, and was surprised to see when I returned that the display was still on. I have the display sleep set to 15 minutes, and the computer sleep set to 45 minutes.

I clicked on the Firefox browser icon in the dock, and the display went crazy. It looked like some sort of weird resolution problem. There were many verticle lines, and the entire display seemed to be vibrating. I could still faintly see all my icons and menu bar, and could still move the mouse pointer. However, nothing I clicked on responded.

I shut down the computer using the power button, and restarted. As soon as it powered on, the video problem was still there. This time it was many green and gray colored verticle lines, but could still see the Apple logo. The rotating spokes that come on during boot up were also visible. Once they stopped, the verticle lines were still there, but changed color and density, and the start up stopped. The Apple logo was still visible.

I shut the computer down again, and disconnected the power cord. After 40 minutes, I powered it back on, with the same results.

I then reset the NVRAM to no avail.

I then restarted in safe mode. All the same display problems were still as described above, but the power up completed. Once the power up completed, the verticle lines changed. Now, there were groups of 6 verticle lines, with each group separated by about 1.5 to 2.0 centimeters. The display colors behind these lines were normal, as were the menu bar items. I opened system preferences, and was able to change resolutions, but the verticle lines were still there. I set the resolution back to "best for display".

I restarted again in normal mode, and it was back to the same problem with the display, and the startup would not complete.

I appreciate any advice from anyone that has seen a similar problem, or advice on a good repair shop. Of course, it may be time to buy a new Imac since this one is already at least 6 years old.

Could be many things.

Video Memory

Main Memory

Corrupt Video Driver

Corrupt Memory Driver

Bad Video Board

Bad Main Board

Too much dust accumulated on the inside

Loose wiring (though not likely)

Circuit degradation from heat

You can generally verify hardware issues by either entering the BIOS setup or Booting from External Media like a OS DVD (and not boot from the Hard Drive) to see if the video problem persists. If so, then this will conclude it definitely being a Hardware Issue.