What GPU did you sold? Yes you could get a 750ti but you have to understand that you aren't facing a compatibility issue here. Your current CPU is too weak and almost all new GPUs won't be able to reach their full potential. Also you shouldn't forget that a lot of modern games don't actually support dual core CPUs anymore (your CPU isn't even a true dual core, it's more like a 1,5 core CPU). On top of that your weak CPU will make a 750 ti behave like a 730-740 in a lot of modern games (remember if you are able to run them).
So in your case you should either get a weak/cheap GPU or consider getting a new more modern system. Also consider that getting a weak/cheap GPU may not give you the performance you expected and you may feel like you lost money on that upgrade. So if I had the money I'd get a new system.