Dell mobo wont start

Got myself a DELL Precision Workstation 410 motherboard. Made an adapter to be able to use a standard ATX PSU for the DELL proprietary 24-pin connector. Testing verifies that it delivers the correct output. However, I cant get the motherboard to POST. No beeps, no signal to the screen. I have tried everything:
- changed video card
- changed PSU
- changed memory
- changed CPU's (matched ones)
- reset CMOS
- removed CMOS battery overnight
All changed HW worked in other computers.

What else can I try to get it to work ?

Does it need to have the fan connected to start ? The CPU's have large heat sinks but no fans.

I don't have a DELL case. Do I really have to put it in a DELL case with a DELL PSU to get it to work ??

Thanks for any comments !!!!

you certainly dont need to have it in a dell case. but it definitely looks like you need their psu. try calling them?

not being funny but did you correctly assemble the adaptor? Could it be inverted?

Thanks for your answers !!

No, I haven't called DELL yet, but I will soon.....

Inverted the adaptor ? Thats a good question. After checking, I can tell you that I havent. The pin numbers indicated in the service manual corresponds to the pin numbers on the motherboard.

There are a few things I suspect:
- Fan header on the motherboard? Does it have to be connected?
- In a newsgroup somewhere I read about a DELL PSU with an extra cable that had be connected to the motherbord. It seems like DELL have a number of different power supply connectors: (1) with a 20-pin ATX-like connector combined with what looks like a 6-pin AT connector. Of course with non-standard voltages on the pins, and (2) with a single 24-pin ATX-like connector. I believe that the message I found was regarding case (1). If not, does anyone know what that extra cable is?

Thanks for your patience !!!