As previously said DirectX and OpenGL are not 2D libraries even if they can be used to for 2D rendering. SFML is something I've worked with, but only during 2 months or so. Me and some friends did a 2D game with it in college last autumn and it was pretty easy to work with. On the other hand I've programmed C++ for 3 years prior to this, so dunno how well you can code and if you can manage SFML.
When I started my first year in college we instantly started with C++ and after 6 months or so we were introduced to a 2D engine called HGE. We used that to make a simple(very simple) game for mobiles. It was 3 years ago so I'm not sure how I would feel about HGE now when I know a lot more, but I remember HGE being pretty easy to use - even as a beginner. But then again, programming was generally confusing at that time so maybe HGE isn't good at all ^^!
Might be worth checking up on, though. If HGE turns out to be too confusing I would really recommend SFML due to its helpful community and its broad usage.
HGE: http://hge.relishgames.com/ There are some example games posted on this link as well, might be interesting to check them out as well.
Good luck coding!