You need a processor that can support more PCI Express Lanes.
The following is an excerpt from Intel website for Intel g3930 cpu:
Expansion Options
Scalability 1S Only
PCI Express Revision 3.0
PCI Express Configurations Up to 1x16, 2x8, 1x8+2x4
Max # of PCI Express Lanes 16
NB. Some of these lanes will be used up by other devices e.g. SATA
Also, as in the previous comment, this is a Bitcoin forum not Altcoin!
Thanks for answering my question, rather than the previous poster who wasnt much help - noted about the wrong forum. I'll have a check in the bios see if theres anything i can disable to free up some lanes!

I checked into the PCI lanes point and its not an issue, plenty of other people are running this board with 13 GPUs on the Intel G3930