Q: Adding second Xeon E5430 to workstation I have a PC with a Supermicro x7dwa board and one Intel Xeon E5430 processor. I tried to add a second identical CPU to the board, but it stops the PC booting. The power LED on the board never lights up, I don't get any beeps, and the CPU fans spin for about one second only. The GPU fan continues spinning, which is powered from the board. I've tested each CPU separately and the PC boots fine. The BIOS settings look good. I can't see any physical damage on the second socket. What other issues might cause these symptoms?
Update: after doing more research, I thought my old 650w psu might be under-powering the board, so I bought a new Corsair HX850i and removed non-vital cards from the board, but it didn't help. Any ideas anyone?

A: My bet is that the two CPUs aren't as similar as they seem. I've barely goofed with setting up multi-CPU machines, but every time I have I've strictly followed a rule on the topic I was taught back in the 90s. The rule is that you want two CPUs that are insanely identical, like down to the serial numbers if possible. CPUs made in different countries with the exact same part numbers could still be a bad pairing. Now, maybe this 'rule' is overkill, but I've followed it all the same and my ~3 experiences with such machines have gone well. 
I suggest you try running the system on each CPU, one at a time. If that works, then I'd think the problem is either the pairing thing I'm talking about, a BIOS issue, a motherboard jumper issue (more something I'd expect from ~20yr old gear) or your PSU as you offered.
I may well be mistaken, but that's the best I can offer. I hope it helps somewhat.

The apparent rationale about wanting parts from the same country was based on the claim that different fabrication plants source their raw materials from different sources and can end up with very superficially different timing characteristics when in operation. Only that 'superficially' isn't so superficial in the case of two CPUs that need to be fairly perfectly synchronized. I personally don't know if this is really true or ever has been, but it sounds kinda sexy.
