GPU's compatibility is determined by the motherboard, same thing goes to CPU. In addition, GPU's compatibility is also determined by the PC case, whether it allows full-height or half-height cards. With that said, almost all motherboard are compatible with every GPU as PCI-E lanes are backward compatible. The only thing I would check now is the PC case, but that would require you to provide the case model with the specific GPU in mind.
Other than what I've said above, you're probably worried about bottleneck too. Some benchmarks have shown that even an Athlon X4 750K (the lowest CPU recommendation for gaming build) won't be a bottleneck to the GPU, but keep in mind that it is still a lot stronger than your Pentium Dual Core 3 Ghz. Therefore, I would conclude that your CPU will matter on graphic performance and will most likely lower the expected performance of a GTX 750 Ti.
There are 3 options now,
1. Leave it like that and use what your CPU can do while limiting the performance of the GTX 750 Ti.
2. Downgrade the GTX 750 Ti to something like HD 7770, R7 250X, or even R7 240.
3. Upgrade the CPU/MB to Athlon X4 750K and a board with total being around $130 for just the CPU/MB, which still need a GPU.