8400 does not power on - no POST

Sorry to hear that. I too have an 8400 that just went out of warranty with fingers crossed. Unfortunately, if your amber light is solid and not blinking, it more than likely is the motherboard. A blinking amber light would have indicated the power supply.

Here is a link to others on this board with similar conditions.

http://forums.us.dell.com/supportforums/board/message?board.id=dim_other&message.id=287831&query.id=51604#M287831

You might want to try of the places they recomend other than dell to purchase a motherboard, which for the 8400 is not that much, around 29 dollars or there abouts.

Had the same exact problem with my 8400 2 weeks ago - system was purchased 12/04. I, too, thought it was my mobo after reading other articles here, so I ordered an OEM replacement from a 3rd party (don't know if I can mention them, so I won't) and tried that, but got the same results. I was able to borrow a P4 530 3.0 GHz CPU, which is the same as what came with the system, and put that in the new mobo and it fired up fine. I took a chance put the CPU in the old mobo and that also worked fine. So, I bought a P4 541 (3.2 GHz with EM64T technology), put that in, and everything's working.

Katnok, hmmmmmmm, never thought of that. I suppose that is possible because it was mentioned that the computer was working before being shipped and then after it was shipped it did not post. There was no mention of over heating prior or lighting storms etc. Might be possible that the CPU became dislodged or lose after being moved around during shipping. Worth a try to take the heat sink off and re-seat the CPU. Of course don't forget the thermal grease between the CPU and the heat sink after doing this. If that does not work, I would still install a new mobo to track down the problem. Of the two, CPU and MOBO. The mobo is only a few bucks, the CPU would be a heck of a lot more. Just a thought.

Thanks for all the input. I tried to reseat the heat sink and CPU - no avail. Guess I will need either a new motherboard or a new processor. Anyone have a system I can scavenge? ;-)
Can I use any newer motherboard/processor combination in the 8400 case (say a newer motherboard with a Core2 Duo processor)?

I cannot speak from personal experience, but I was under the impression that Dell cases won't easily accept off-the-shelf mobos from a fitment perspective. I'm sure someone can vouch for that.

As for the OEM replacement board, you can get one easily for ~$40. I was able to get the 541 CPU for $138 shipped and that was for a factory sealed retail box, although I *thought* I was buying a 540 (same thing, minus the EM64T technology). But, the BIOS recognizes the 64-bit CPU, so all is well.

Okay, so an upgraded motherboard/processor combo is out of the question? What a pity. Thought a dead Dell was a good excuse to spurge on an update! Too bad. propritary cases :-)
Thanks again for all the suggestions.

Thanks for everyone's input. Turns out it was the MB, and as suggested, have ordered the replacement from the company mentioned in earlier posts. Shall hopefully post a triumphant message from the newly resurrected computer soon :-)

CaptRock,
I had no spare parts lying around, so I took the machine in to our computer services dept. and had them check it out. They said that the processor worked fine in another machine, so it had to be the motherboard. Believe it or not, they quoted me $275 to get a new one in! Told them I would get them the MB and they could just swap it in. Now, if I can convince the Mrs. that it actually cost $275 to fix, I would have some spare change lying around to spend on new gadgets! :-)

Good point! I shall have to make sure they (they - i.e., the computer services people) put some fresh thermal compound on. And hopefully, they will not charge me an arm and a leg for it!