We've all been there. You had what you thought was an idea, you started, plotting, writing, jotting, whatever is your process, you're all excited and then...you have an ellipsis trail that never picks up.
Maybe you can't figure out what your character's big secret is.
Or you don't know where he'll find the solution, or even what the solution is.
It's easy making messes for our characters, it's harder to clean them up.
My counter-intuitive suggestion is to stop trying, and go DO something. My second suggestion is to take a shower or do dishes (there's something about water that just makes the mind flow). But vacuuming and raking and running will work as well. Yes, I'm being totally serious here.
When you stop actively trying to solve a problem and then do something your mind doesn't have to give much attention to, it's an opportunity for your subconscious to come online and work its magic.
I can't tell you how many plot holes and dumpster fires I've worked through like this.
The only downside is my water bill