MacPro mid-2010, Mojave, Geforce GTX 680 "for Mac"

If you get the genuine Mac version of the GTX 680, it works perfectly. There are lots of PC versions out there that have been flashed by the user, but don't always work as expected. Mainly, you don't get an image until your Mac gets to the desktop, and you can't do an Option key startup (because there's no image to see what you're doing).

I had one in the same model Mac. It worked as expected. You don't need to install any drivers. The OS supports the true Mac version directly. My card is actually for sale, but haven't listed it on eBay yet. I have my 2010 Mac Pro up for sale after putting the original ATI HD5770 Radeon card back in.

What you want is this specific version of the card. Don't bother looking at any other version of the GTX 680.

Yes there is no Mojave driver, but it won't do any harm if you want to install it.

Make sure the card is properly seated, lay the Mac on its side to insert the card.

Is there another Mac you can try the card in to try and eliminate that it might be a problem with the Mac.

Ask them it's not messing about, it is vital research.

Are you able to try all the display connectors.

Have a look here if you want, https://www.geforce.co.uk/drivers

USB won't get you any kind of video signal. Did you mean HDMI?

The GTX 680 has four display connections, two DVI, one HDMI and one DisplayPort.

My MacPro has an Nvidia GTX 680 (flashed for Mac) all you do is put it in the bottom PCIe slot, connect the two power cables

to the card then the to the motherboard. No need to install drivers. Power up your Mac and it should be good to go.

Is the card showing up in System Information> Hardware> Graphics/ Displays.