Dual Processor - Only showing one

Can you post a little more information like service tag etc. Did you upgrade the server or was it initially a dual processor.

What LEDs are lit on the system board ? There are 6 LEDs located at the rear of the system board behind the PCI slots.

Check the LED state with power and also in standby mode. i.e. powered down but with input AC power on.

I would recommended updating the bios, BMC/esm firmware.... it could be the micro code for the procs causing that

Where is it only showing one? In the task manager, bios, or at start-up?

 

I had a similar issue where my second processor died, it still booted, not much I could do about it, short of getting a new one.

 

Try taking one processor out and identify which one doesn't show. Starting Windows with the good one, let Windows identify it as a single processor box, then put it back in and let Windows identify it as a dual processor box if possible. Just the process of removing and replacing it might help fix a loose processor or something up with Windows. 

 

If you talking about in the task manager, are you sure you don't have View -> CPU History -> One Graph, All CPU's checked? Just a thought.