Using Pcie x4 slot on a T1700

I have a T1700 with a Xeon E3-1246v3. This cpu has HD graphics so I have all my pcie slots available.

There are 3 pcie slots:

1x pcie x16 slot gen3

1x pcie x16 slot wired as x4 gen2

1x pcie x1 slot gen2

I'm running into problems when installing 2 pcie cards: a Dell H310 and an intel quad port nic.

If I install just 1 card in the gen3 slot, any card works fine.

If I install 2 cards, one in the gen3 pciex16 and one in the gen2 pciex16 (wiredx4) the card in the x4 slot does not work. If I switch the cards the same happens: the card in the x4 slot does not work.

If I install only a card in the x4 slot, it does not work.

Strange thing is that the card is detected in the x4 slot (name ...) but somehow it is not active so no drivers load.

Is there any setting in the BIOS I have overlooked so activate the x4 slot (or that interferes with the working of the x4 slot) ??