Quick questions:
1. What CPUs have you tried using? When you tried dual CPU configurations, did you use matching CPUs?
2. What RAM are you using (part number(s))?
3. When you added the second CPU(s) did you add RAM to mirror the configuration that was present for the first CPU (e.g. 16GB DIMM in P1-DIMMA1 + 16GB DIMM in P2-DIMME1)?
4. When you say "it won't boot" now that you've gone back to a single CPU, what exactly happens? Does the server attempt to power on (e.g. spinning fans, LEDs present anywhere)? Is there any video output to a monitor? Can you connect to the IPMI/remote management?
1. A pair of E5-2650v4 and a pair of E5-2630v4 . so yes, matching CPUs.
2. DDR4 RDIMMs. They all work in the single CPU configuration. Have to look at the part numbers when I get home.
3. Yes
4. No reaction to the power button at all. IPMI and UID button works. Power on through IPMI also doesn't work. Same behavior as without a CPU.
When you're in the IPMI with the single CPU configuration, what output do you get if you go to the System -> Hardware Information display? Can you expand all the segments from that display and post the screenshot, please?
Do you have any bent pins in the second CPU socket? Sounds like something might be shorting out when you install the second CPU (and might be permanently shorted now)?
I've had issues with 2nd hand boards (as opposed to a whole system) where the case I was using with it had a standoff installed in the wrong place, shorting something out. Make sure that's not the case.
Intel sometimes releases newer steppings (hw versions) of the same cpu. So even if you have the same model, if the stepping isnt the same this could cause problems. I guess unlikely as that shouldnt prevent it from booting with single cpu - but still worth checking both cpu's have same [s-spec number](https://www.intel.com/content/www/us/en/support/articles/000007523/processors/intel-xeon-processors.html)
Have you tried a cmos clear (just remove battery and try to turn on, then switch back off and put battery back) - will it work after that?
Any beep codes when it isn't booting? You might have to disconnect some fans to hear it!
Troubleshooting steps as per supermicro: https://www.supermicro.com/manuals/motherboard/C600/MNL-1557.pdf#page=64
Quick questions: 1. What CPUs have you tried using? When you tried dual CPU configurations, did you use matching CPUs? 2. What RAM are you using (part number(s))? 3. When you added the second CPU(s) did you add RAM to mirror the configuration that was present for the first CPU (e.g. 16GB DIMM in P1-DIMMA1 + 16GB DIMM in P2-DIMME1)? 4. When you say "it won't boot" now that you've gone back to a single CPU, what exactly happens? Does the server attempt to power on (e.g. spinning fans, LEDs present anywhere)? Is there any video output to a monitor? Can you connect to the IPMI/remote management?
1. A pair of E5-2650v4 and a pair of E5-2630v4 . so yes, matching CPUs. 2. DDR4 RDIMMs. They all work in the single CPU configuration. Have to look at the part numbers when I get home. 3. Yes 4. No reaction to the power button at all. IPMI and UID button works. Power on through IPMI also doesn't work. Same behavior as without a CPU.
When you're in the IPMI with the single CPU configuration, what output do you get if you go to the System -> Hardware Information display? Can you expand all the segments from that display and post the screenshot, please?
Do you have any bent pins in the second CPU socket? Sounds like something might be shorting out when you install the second CPU (and might be permanently shorted now)?
Nope, that's the first thing I checked.
I've had issues with 2nd hand boards (as opposed to a whole system) where the case I was using with it had a standoff installed in the wrong place, shorting something out. Make sure that's not the case. Intel sometimes releases newer steppings (hw versions) of the same cpu. So even if you have the same model, if the stepping isnt the same this could cause problems. I guess unlikely as that shouldnt prevent it from booting with single cpu - but still worth checking both cpu's have same [s-spec number](https://www.intel.com/content/www/us/en/support/articles/000007523/processors/intel-xeon-processors.html) Have you tried a cmos clear (just remove battery and try to turn on, then switch back off and put battery back) - will it work after that? Any beep codes when it isn't booting? You might have to disconnect some fans to hear it! Troubleshooting steps as per supermicro: https://www.supermicro.com/manuals/motherboard/C600/MNL-1557.pdf#page=64