Did you server have 2 PCIe slot (1 LP and 1 FH) or 3 LP PCIe Slots. As Young E mentioned all PCIe slot will not be working when you have only one CPU installed on the server. If you have 3 PCIe slot server then Slot 3 only work with single CPU. 
Hi all, I have a problem whereby all 3 units of my newly purchased refurbished R620 servers were not able to detect my ConnectX-3 MCX354A-FCBT 40Gbps card (non-Dell, but Mellanox). For all the servers, I have updated with the Platform Specific Bootable ISO, PER620, 21.07.00, and tried the official Mellanox ConnectX-3 and ConnectX-3 Pro Ethernet adapter Firmware, but with no avail. Totally not detectable via iDRAC, or even LCC > Hardware Configuration > Hardware Inventory >View Current Inventory. No LED blinking either on the card. Installed the NIC on the PCIe Slot 1 with single processor configuration, and happened the same with all 3 servers. Any idea what is the issue? Meanwhile, still trying out the DELL EMC Server Update Utility to see if it fix... Thanks.
Dell R620 not able to detect Mellanox ConnectX-3 MCX354A-FCBT 40Gbps NIC