I've finished my master's program. How can I improve my credentials so I can do a PhD?
I had a student who was, if not exactly in your shoes, certainly "disadvantaged" in being able to make it into grad school. Normally, I would just not respond and file away a cold call like that, but reading his email, which was asking for a chance to do research (not even paid—just work doing something related to research), and had a strong vision of what he wanted to do in the future, that it resonated with me. It also just happened that around the same time, I had some ideas I wanted to try out, and a small bit of funding available. So I offered him an internship that would be able to pay his living expenses, and gave him a shot. Today, he's thriving as a  PhD student in an aerospace engineering program in Europe. 

So there's always a chance. The best thing to do is to get research experience. Once you can get some people who can comment "don't worry so much about user92705's grades, because user92705 has done really well working in my lab, and I know will become a good researcher," it will go a long way in getting you into a graduate program.