I have an older Dell Presision 650 Xeon that was given to me by a friend. I'm currently using it as my primary and decided I wanted to max it out.
It has dual core capability, so I grabbed a matched pair of Xeon 3.2Ghz Intels from ebay plus a VRM and a second heatsink from someone else on ebay.
Put the first 3.2 in and it works great.
Put the second 3.2 in, heatsink and installed the VRM.
When I powered on, the screen remained blank. It was making a "click click" noise and the little LEDs were like so: a=flashing yellow then green b=green c=yellow d=yellow.
I've looked around but can't find much documentation for this. The only things I can think of are the second processor is bad, or the VRM is bad, or there's a jumper somewhere that needs to be changed.
Use the good cpu and go into the bios using the "del" key at posting, and see if you have any settings to change. But be careful and don't change too much, or the board may not post. Then you'll have to reset the bios using the cmos jumper or by removing the board battery with the system turned off.