Hi there...Your problem used to be my problem (and still is on occasion).
I realised after several years that my problem was I was trying to come up with an original idea...don't bother because it has all been done before, in one guise or another. once you realise that it is your characters and your settings and your style of writing that makes a piece unique pick any plot line you like.
boy/girl meets girl/boy, boy/girl loses girl/boy, boy/girl does something heroic/stupid to get girl/boy back etc
Warring siblings are brought together by the terminal illness of one, or of parent, spouse, pet
small band go on a quest in order to find something that will defeat terrible overlord
Just open up a film guide and pick one! You generally find that once you start, new ideas come to you to give you a new slant on an old theme. Good luck to you.