No AHT when I hold down D

No, I just meant that your Mac is confirmed as being mid-'10. It shipped with 10.6.3/4 That results at that link were for someone who upgraded. EDIT: Or at least I assume it is. I don't know how that site operates.

Message was edited by: WZZZ

That results at that link were for someone who upgraded. EDIT: Or at least I assume it is. I don't know how that site operates.

Correct - the people submitting their results simply enter their exact configuration. A mid 2010 did come with Snow Leopard and, as far as I know, you do need your install disks for AHT.

That model's files are in the package mentioned, so should now be at /System/Library/CoreServices/.diagnostics/Mac-F2238AC8 on your computer ( .diagnostics is invisible as standard, due to a leading . in the name).

It's an iMac11,2 : mid-2010 & should have shipped with a build of 10.6.3/4 as you've been told.

If iMac EFI Update 1.8 has been installed (how to check), then you should be able to use Internet Recovery, although a hardware test, if available there, may not support that model.

The download you used has worked for many, I can't check it for your model. If you waited several minutes & were unable to start the test proper, then I now see there's a direct from Apple link for it at

http://download.info.apple.com/Apple_Hardware_Test/022-4703-A.dmg

which I'd overlooked earlier (my apologies); although the relevant model-specific files appear identical. Still, it can't hurt to remove those downloaded earlier & try that one instead.

You can remove it , just trash the /System/Library/CoreServices/.diagnostics folder, or its contents if preferred.

I'm hoping to get hold of the original disks

You can get a machine specific replacement disk by calling Apple for a nominal fee (they'll need your serial number).

Just a tip: If you can somehow get ahold of a copy of the ASD (Apple Service Diagnostic) for your Mac, it will be far more worthwhile than the AHT, which, though better than nothing, has a reputation for being extremely unreliable. But, naturally, stay away from any torrents or any untrustworthy site for this because there may be malware included.

I think you just let it run through and get the results. What you do with the results may be quite another thing.

Scroll down to near the end of page 2 of this thread for an idea.

https://discussions.apple.com/thread/4996559?start=15&tstart=0

But this is not something to be farmed out to just anyone. It needs special skill.

Logic Board>Graphics Card>Graphics chip on Graphics Card.