need help pci-e x1?

[phawkins576]

hi guys, recently got an asus a8n sli deluxe skt 939.

When i was setting it up and had my 7900gs in the blue (top) pci-e slot, there was no signal coming from my card to my screen.
So i put the card into the bottom slot (black) and tried it, it worked fine. But now if i run graphics-z, it says my pci-e is running at x1 and not x16 like it should be. Is this because the bottom slot is only used for sli cards and the top is the primary slot?
If so how do I get the card working in the top slot? Do i need to change anything in the bios.

This board was 2nd hand so maybe the person who had it before me has changed some setting? Or is there a common problem with the x16 slot at the top breaking?

 

[Sean_UK]

Used to have one of these boards and iirc you could use either single slot (Both are true x16sli slots), providing some option in bios was changed, cant remember what option it's under, sorry.