You can use liquid nails for subflooring or for concrete flooring, but you need and must also use the nails. During the curing process and stretching process, the liquid nails will loosen and the carpet will not be tight.
If you are having trouble seating the nails in concrete, join the club everyone does. The key is to only hit each nail once. the second for good measure hit only loosens the nail. One hefty hit is all you can do.
Now if you are not good at aiming and a powerful one time hit, then buy a 22 concrete nail driver and seat the tack strip with this tool. Drive one nail about every 8 inches. Use a low power cartrige and a short nail.