Burned motherboard

Hello I have two new PCs they are made by Micronet are some of the schematics
Intel 1.8MHz
Intel Motherboard and Chipset (D875PESV)
Samsung 60gig HD
256DDR
300 Watt power supply

The PC had been previously working. I took it apart and put them together for a "learning" experience (I got one alright).

When I plugged the PC back in within 60 seconds the motherboard started smoking I unplugged it at that point. (Keep in mind the PC was not on it was just plugged in, getting the 5 Volts from the ATX power supply). The motherboard now has a burn mark on the IDE connection and next to a resistor very close to the IDE connection.

I took the good PC and tested out the good motherboard in the bad PC (Nothing worked leaving me to say that Power Supply was now bad)

I then took the Power Supply from the good PC and plugged it into the bad motherboard. The green power light came on the bad motherboard (just for a second) and now the good power supply no longer works.

What could I have done wrong to get this to happen in the first place? My only thought is that I have an 80 Pin cable for the HD and a 40 Pin cable for the CD-ROM is it possible that mixing up the cables(putting in the wrong IDE connection)s do this?   Please not the connections where not forced into a place they could not fit.

Also is it possible that this now bad motherboard can fry good Power Supplies (two of them)? Thanks for your help.
langdjAsked:
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jhanceCommented:
1) Mixing up 80 and 40 pin IDE cables or even reversing them WILL NOT burn up your MB.  Something else happened.  My guess is that you either plugged the power or some other connector in wrong or into the wrong place or you somehow shorted the MB to the case when you re-installed it.

2) A bad MB CAN indeed fry good power supplies.  

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langdjAuthor Commented:
What is the MB doing to fry the power supply. Any thoughts?
jhanceCommented:
Whatever damage has occurred to the MB must be presenting some type of load to the power supply that it's unable to handle.  It's had to say specficially but the most likely issue is a short-circuit of some type.
jhanceCommented:
Hey, thanks for accepting my comment but it would be really great if you would fill us all in on what you discovered to be the actual issue.
langdjAuthor Commented:
No problem. If I do get to the bottom of this I will post my thoughts thanks.
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