Your CPU is Intel Pentium dual core G620 for LGA 1155 correct ? this CPU is to weak for GTX 750Ti
You can grab i5 CPU for this socket for around 65 $ or i7 80$ on ebay
What mobo you have ? you can use CPU-Z to check this
http://www.cpuid.com/softwares/cpu-z.html
What PSU you have model, brand and how old is ?