Model A1225 / Mid 2007 and Early 2008 / 2.4, 2.8, or 3.06 GHz Core 2 Duo processor

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No display and failing to boot.

I have a rather interesting problem with my iMac. A few weeks ago the screen stopped working, however I use this computer almost exclusively through screen sharing from my MacBook and it wasn't really a huge issue. I have just been on holiday and on my return the computer will now not boot. I have the boot-up sound and can reset the PRAM and get the second boot-up sound. The DVD drive is spinning up when a disk is inserted, however the computer is failing to appear on the network.

I have tried plugging it into an external display and there is no display shown. I have inserted the original installation disk whilst the computer is plugged into the external display and an image is then displayed (however I think it is set up to extend desktop - so only the background appears). I am wondering whether I now have two problems and whether these could both be linked to a cooling issue.

I imagine due to the fact that I'm getting a picture on the external display when the installation disk is inserted that the video card is working properly - does this then mean that the LCD is broken - how much is this likely to cost to replace. The screen glows when the computer is turned on and goes back black when it is switched off.

Secondly, I imagine that due to the fact the computer is no longer appearing on the network - and only appears to boot from the installation disk that my hard drive has failed. Is this a correct assumption?

Thirdly, I imagine I would be pretty unlucky to have both these failures within such a short time of each other, so are they likely to be related to a cooling issue?

Many Thanks in advance for your help

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When you state the external is showing my desktop when I boot-up under the recovery disk are you seeing a textured background or just a blue background also can you slide the mouse over to the external display so you can see it? You'll likely need to try both left and right directions and up and down. Then try creating a folder using the mouse controls. Any luck?

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I may have misled in my original post with my comment about extend desktop - all i meant was that not seeing the normal options that apply when inserting the apple installation disk ie. the external display is acting to extend the desktop not mirror the image on the imac display. Its not showing my desktop, just a default apple picture background, Yes I can see the mouse, seems to be on extend desktop mode, over to the right hand side. I have no options on right click, but wouldn't imagine that I should at this point of the apple installation disk. Hope this helps - thanks for your help.

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Let try the basics here as this is very odd set of problems:

Try resetting the SMC Apple TN on resetting the SMC anything change?

The next thing I would try is getting AHT running hopefully it will display on your second screen now Apple TN on AHT any luck?

OK still can't get anywhere lets try accessing the diagnostic LED's At this point we need to open the system. Here's the iFixIt guide on getting to them and what they mean iFixIt guide on Diag LED's

Let us know what happens and what you find

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Sounds like a hard drive failure first. Boot up from your system installation disk (with the external monitor connected) and see if you can use Disk Utilities to see and repair the hard drive.

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That's great - any idea how I get the external monitor to mirror display so I can read what should be on the screen? Only seeing a picture background at the moment on the external display.

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remove internal display signal cable, desktop will switch to external screen, will see apple logo upon boot up

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Jonathan Dorey will be eternally grateful.
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