It hasn't been possible to break even on Bitcoin (or any other SHA256 coin) mining with GPUs for a few years now.
It hasn't been possible to break even on Litecoin (or any other Scrypt coin) mining with GPUs for about 2 years now.
It is possible to make a profit on mining other altcoins like Dash with GPUs, but you better have some fairly cheap electric and a well-optimised rig.
If you're using the thing as a space heater (essentially free), Dash can make you a bit if you run it on Nvidea Maxwell-based hardware (like your 750 Ti), and a very small bit on recent AMD hardware. You might even be able to achieve RoI on the cards given essentially free electric, but that is iffy.
Don't bother with trying to mine on CPUs at all. GPUs are tens or hundreds of times more efficient to mine with, if you can mine with the GPU at all.
https://bitcoinwisdom.com/bitcoin/calculator can give you some idea of the real numbers.
Even if there was an alt-coin that was still profitable to mine with GPU's, Nvidia cards really suck at it
Badly outdated info, CURRENTLY the Maxwell Nvidia cards are the BEST to mine with on most altcoins, the pre-Maxwell ones aren't as good as the Maxwell ones but are sometimes competative with AMD cards depending on the specific algorythm the coin uses and how recent of a version of the correct miners you use.
