your scores doesn't submit ? you are probably having internet connection problems, look into that.
judging from your profile stats you're like my friend who loves to play beatmaps out of his league resulting bad overall accuracy.
the thing is its not about fcing or finishing a ridiculously hard map but its all about having a really good accuracy say 96%+ to gain enough pp.
I remember the time when I just keep on playing saiya remote control insane I was like 320 combo on it ranking B how much pp it gave me ? well 5 or 6 iirc, almost to no worth. I know its not an FC, a good example though. besides how can you say FC when you rank B or C on some maps unless you are consistent at clicking 50's.
TL;DR: improve your accuracy, settle for easier maps for now.
and also if you are picky with songs then download as many beatmaps as possible. you might find few to your likings which you might do extremely good at it and gain pp easily.