The case of the disappearing NIC [Solved]

So I've got a HP DL380P G8, I have an Intel X540-T2 in it and all was merry. However, suddenly after about a month it no longer exists. Doesn't appear at boot either, the iLO reports that there is nothing in that slot.
However if I take the card out and put it in another machine it all works perfectly.

Does anyone have any tricks I could try? I've swapped PCIe slots and that didn't do it. Tried shutting down and cutting the power for a few minutes, also didn't work.

I've also got a second gigabit nic that works fine in all the PCIe slots.

Any suggestions you guys come up with would be appreciated, thanks.

Does it stay up for long period of time in the other machines you install it in?

You're right, when I chucked it in the other machines I basically just checked to see if it was detected.

When used it just keeps disappearing and reappearing, much like unplugging and plugging in a USB. So it is borked. The HP server must be doing a pretty thorough post check to decide that it is dead and just not bother with it.