I searched your mobo in google and find
this site and i looked into your specifications of your mobo and find this:
1 x PCI Express x16 slot, running at x16 (PCIEX16) (Note 5)
(The PCIEX16 slot conforms to PCI Express 2.0 standard.)
1 x PCI Express x16 slot, running at x1 (PCIEX4_X1)
2 x PCI slots
As you can see your second gpu slot is a x16 slot but is only running at x1. So this means that this slot isn't intended for your GPU. You really need a new mobo that got 2 x16 slots or (1 x16 and 1 x8 slot) and also with SLI support.
I also searched the net for you for a good motherboard and i only found
this one. But this one only supports i5/i7 cpu's.
Its really hard to find a mobo thats supports sli, LGA 1156 and i3 CPU and also cheap.
I should save some money and buy a LGA 1155 motherboard thats support SLI and a new i5 or i7 CPU.