Hi,
 
    I have an old Dell Precision Workstation 450.  It has a single Intel XEON 2.4GHz cpu inside.  I've got a second Intel XEON 2.4GHz cpu that I'm trying to add inside since it has a slot for a second cpu.  The 2 cpus are the same family and are both in working condition when in single cpu mode.  But when I put the second cpu inside, the system won't start/boot.
 
Any ideas ?
 
Thanks

Are you running a server OS or normal one? windows xp home and I want to say vista (correct me if im wrong) doesnt support multiple CPU's, though im assuming your running a server OS due to having the ability of multiple CPU's.

Did you add a Voltage Regulator Module (VRM)?
 
It's a small card that goes in the slot between your second CPU socket and the AGP slot - you got to have one for 2-CPU operation.
 
If you don't have one, I'd try ebay as new ones are ~$80:
http://www.impactcomputers.com/4k666.html
 
 

 
Check the second cpu and vrm on their own to verify they work before you add the second cpu.
 
Verify psu compatibility.  If the mobo manual 'recommends' eps 24-pin & 8-pin connectors it pretty much is a requirement.
 
WinXP/Win2k Pro or a 'Nix needed to boot into OS.
 
Does that workstation require ecc ram ???

Its probably the VRM card, its missing...  Thanks for your help!
 
UPDATE: It was the VRM card, workstation up and running!