Mac N00b with Power issues and Questions

Hello all. I am new to these forums. I am a PC guy. Been a PC tech for the last 10 years. I am use to figuring out PC hardware and software issues, but dealing with Macs are sort of a new animal to me. I can work my way around them just fine and even do a decent amount of support for them as I have had to in the past. I had this 2006 iMac in the shop that the customer said they were burning a disk and then it stopped working. I tackled this beast and did some preliminary checks. It would not power on at all, no lights or sounds or anything. I ended up taking it apart and inspecting the internals looking for any sort of burned out components, or any thing out of the ordinary. The only thing that I know of that was done with this computer was that the HD was failing not too long before this and was replaced(by my company) and all was fine until the new issue of it shutting of during a disc burn. I was taking some readings of the PS and Inverter but was unable to find a source to tell me what voltages I was suppose to get. I didn't want to buy parts that would not fix it if I didn't have too. When I ended up putting it back together, I was finally getting a pulse glowing light from the bottom right hand side, but nothing else. At this point I figured it had to be either the PS or Logic board that was the issue. I told the owner what it was looking like to possibly fix it and it ended up back on the shelf and sat there for the next 7 to 8 months. I finally got back in touch with the owner and they basically told me they got a replacement and they didn't want this one anymore and we could recycle it. Now my wife has been getting into photography and journalism over the years and was wanting a iMac of her own. I can't afford a new one at this time so I was able to get a hold of this one to try and fix. Well I plug it in at work, hook up a keyboard and mouse, press the power button and it turns on, just like that. Seemed to work flawless for the next few days. Bring it home, work on getting it ready for my wife to use. Is on basically all weekend, shut down turned on, restarted. Even used a TechTools program to make an edisk and do some optimization. Got it all set for the wife when she returned on Sunday. I go to show her and It doesn't turn on. Let it sit for a few unplugged, nothing. Let it sit unplugged for a longer amount of time(hour or two), go to turn it on and it turns on. When we went to turn it on tonight, sill turns on fine.

Anyone ever experience this? I am sure it is something with a component on some PC board inside but I don't know if it is the Power Board or the Logic Board. Any and all help is appreciated. Thanks.

*Edit - Also forgot that I am not able to run the AHT, but I want to badly. There is no ./diagnostic folder on the drive and I don't have a Application disk as all this came with was a retail of SL 10.6.3 and that didnt boot to any diagnostics. This also has an intel cpu. Thanks.

G'day and welcome tot the forums.

Apple Hardware Test is on disc 2 of the discs that shipped with whatever model iMac, Mac Pro, MacBook, MacBook Pro or Mac Mini you are using ~ the thread does not say what model. You would need to look at eBay and such for the precise set of discs from that same model.

Sure sounds like a power supply program however.

It is an A1174. The only disk I got with this is, from what I was told, is a retail disk. Had the picture of a Snow Leopard on it and not the 2 sets of grey disks

The fact that (if I read that solid block of text correctly) the machine will turn on and function normally if start from a COLD start suggests that perhaps the fans aren't working and the machine shuts itself down to protect the processor ... and of course won't start up again until the machine is "cold."

Apologies for the solid block. I was writing from my tablet and it was tedious to write what I did and figured I could get away with this just this time without a comment. It appears I was wrong.

It does not and has never just just off as if it were overheating. Just does not start after it is turned off normally after what seems is an extensive time plugged in and being used.