iMac 20" early 2008 no longer booting



I have an iMac early 2008 which was working just fine but one day and for no apparent reason would no longer boot. The progress bar reaches about half way then the screen turns into a lit, blank page. The iMac won't complete booting.

I cleaned installed the internal drive with El Capitan but get the same result.

I boot with a cleaned installed external disk with El Capitan but get the same result.

However, I can complete booting and use the computer in Safe mode.

Any idea on how to fix this?


iMac 20 inch Core 2 Duo (Early 2008), iMac8,1


Staff member
There are several things to consider and try. The first thing, even in 2019, is to "clear the PRAM". Start the computer and immediately hold down Command, Option, "P" and "R". Keep them held down, until the iMac's boot sound appears for the third time. Then let it boot.
If that doesn't work, there's hardware failures to consider. While there's a diagnose mode (starting up with the key "D" held down), that only goes so far. An authorised Apple Service Provider has more tools that really test for each component of the computer – and I'd ask them if they could run the tests. (Ask them for the price of the diagnose, of course, beforehand.)
The real problem with a hardware failure would be that for a computer this old, Apple doesn't provide parts any longer. Which means you'd have to find used parts for a repair – and afterwards, it'd still be a computer from 2008. So unless you're considering to keep it fit for a museum, an inexpensive used computer from 2014+ might be the way to go, should there really be a hardware problem.


Hi, thank you very much for the information and suggestions. I had cleared the PRAM. I have been busy trying different things to diagnose the issue after my first post. I ran the Apple Hardware Test and a third party diagnosis app which found no issue. It turns out, a failed GPU is most likely the culprit. Vertical bars appears in the display. I remember a similar issue with a 27" iMac a while back. I am doing the work for an older lady but it looks like she will need a new machine...