Mobo help

It might, it will go in the blue one on the left with one long and one short part, the only thing is that the mobo might be a bit too long out beyond that point, so it won't fit. I'd suggest to just get a new mobo at the same time just to be safe, it doesn't look like it will fit.
According to the motherboard specs that i found on asrock's website, it should be fine, as it says the mobo supports one PCI Express x16.
But it is still a pretty bad motherboard, get a new one.

As said, the blue PCIx16 slot is the one you want for GPU's, but be very mindful of space inside the case. Sub-ATX mid boards usually only go in sub ATX mid cases, so the GPU will hang over the side of the mobo quite a bit so make sure there is extra room beyond your mobo for the card to fit.