Trust me, I know that feeling. My best way to get over writers block is to read other stories. Now, I'm not saying steal their ideas, of course, but maybe if you ever read something, and you imagined it could've gone another way, thats (kinda) an idea right there! I think the best way is to make something go your way. Like, 'If Sissi went to Lyoko, what would happen?' Or, 'If Jim rather did talk about it, what would it be?' that one could be drabbles.
'If Yumi went with William.' 'If Odd, or Ulrich or someone else was XANAfied instead of William.' 'If XANA was on their side for a change.' 'One of XANA's attacks was a gender bend attack.' 'Sam became a Lyoko Warrior' One of the best ones I know is the Next Gen. What if their kids got the same fate? What would happen. Switch up the pairings, add drama, romance, angst. Do whatever you want. The world is a piece of paper. You just gotta know what to write on it.
Feel free to use any of these ideas.