The current options for external graphics cards for desktop PCs are discussed at the following article
See the article at the link below.
http://www.pcworld.com/article/3048401/computers/how-mini-pcs-and-external-graphics-cards-could-hera...
Considering the configuration of your PC and the installed Pentium processor, no matter which graphics card you install the video will always be below average.
I suggest saving up for a PC with some power.
For your next desktop PC, I highly recommend that you choose one that has at least an Intel Core i5 or i7 processor and 4GB or more installed memory.
It really is not worth investing into an entry level productivity PC such as the one you have.

I am not an HP Employee.