Asus P5K Pro does not detect 3rd GFX card

[tadpole]

I updated my gaming rig and started using my old Asus P5K Pro motherboard (p-35 north bridge) as a dedicated mining rig.  I've individually tested all the risers and gpu's I bought and I know for sure they are not the problem.  My motherboard will not detect a third card.  I've tried tweaking a few things in the bios but had no luck.  Does anyone know if there is a way to get the third (and eventualy 6th) card to be detected?  If not, can anyone recommend a cheap reliable mobo that will run 6 or more gpu's?  I'll be purchasing one tomorrow if i can't get what i have working.  I've let this gpu sit to long not making me any money.
Thanks in advance.

[jazarja]

you need to use pci-e 1x jumper cable. Working properly with my ASUS P5K Duluxe

[SpeedDemon13]

Most of those older Intel mobo's need a jumper on the 1x pci-e slot. I have a mining rig with a p35 with a core2 quad and had to run all 1x to 16x risers on all slot to make all the cards work. I tried to run 4 1x to 16x and one  16x to 16x, only worked for 2 cards.