PCI Slots - Can't get network cards to work

[Conrad11]

Hi there,

I have an old PC that i am trying to install some network cards on. I have two network cards and they are both working. When i put them in and switch on the pc, I can see a light blink when its switched on but when i get into windows they arent detected?

What am i doing wrong? What could be the solutions?

Thanks.

EDIT: I think its the PCI Slots, I switched one of the cards to a different PCI slot and it seems to be working.