Can I ask, what's your cross-over story about?
I don't really have a problem with writer's block anymore, but when I did have it, it was usually because:
1. My real-world environment + routine was stressing me out, so I wasn't motivated to write.
2. I didn't know what I wanted to do with my story. I would try discovery-writing, aka writing without a plot. In my opinion, it's all right for some chapters to serve as a "bridge" for the next major event in the story, but there should be something noteworthy happening in some capacity, such as a new character being introduced, or, in my case, my characters are falling in love, so I try to use cliffhanger chapters.
3. It's important to also identify your characters motivations (what they WANT, what they NEED). These don't have to be genius-level. Your characters don't need to reinvent the wheel, they just have to have a reason for deciding to go from point A, to point B.
Some context: My character Nika is a 20-year-old 'alien'. In her hometown, there are two, week-long festivals, like the Carnevale of Venice, Italy. These are held twice a year; one in spring, and one in fall. 'Traditionally', a girl would invite the boy she likes to accompany her to the festival, but Nika has never gone with a date before. If I made her follow her usual patterns, she'd never go to the festival, and that would be less-interesting (generally-speaking). So for example, in order for Nika to get from working in her Geranium garden, to playing festival games with her date, there needs to be a specific motivation that propels her out of her comfort zone. Maybe another girl wants to ask the boy Nika likes, and there's a race to see who can get to him first? Maybe there's something special about this boy that fills one of her desires (again, what she WANTS)?
Hope this helps a little. Just a couple things that helped me focus on why my stories weren't working for me, and how to fix them.