Check that you have the latest drivers for nVidia installed.
thanks, it fixed the issue my gpu detection issue.
I get 8 mh/s for one 750 ti.
Still not bad, however 750Ti advantage seems to be reduced in comparison with qubit algo.
Now it is slightly below R9 270 (8,3 Mh/s). Well, 750Ti is low wattage card, so it is still more profitable...