I bought a ThinkCentre M71e (3134-C4U) with the intention of using it connected to several separate physical networks. I bought a PCIe Network card (SuperMicro AOC-SG-I2) with two additional network ports to use for this purpose. As far as I can tell, this network card should work with no problems - it's a PCIe 2.0 x4 card, which should work in the system's PCIe 2.0 x16 slot.
However, the computer does not recognize that the network card is there! To test whether it is an issue with the card, I pulled a similar card (known working HP NC360T) from another computer, and this computer did not recognize it either!
What can I do about this? The computer is useless to me without the additional network connection.
I noted that, while the specs explicitly say "PCI Express 2.0 x16", the Hardware Maintenance Manual calls it a "PCI Express x16 graphics slot" (emphasis mine). Does this mean that Lenovo deliberately prevents cards other than graphics cards from being recognized in this slot?
UPDATE
I have now tested both cards in a ThinkCentre M90p (despite the model number, it's about a year older). The SuperMicro card does not work in that one, but the HP card does work. (So it could be that the SuperMicro card is dead, but that doesn't explain why the HP card works in one machine but not the other.)