Set the story aside, work on something else for a while. Or, if you're writing in a linear mode, try jumping ahead to a future action or scene that you have in mind, and see if that draws the earlier characters into the right direction. I currently have a 5000-word draft that needs some sex punched up and has two draggy middle sections, which I can't get myself reconnected with enough to deal with those. I also have a 3400-word where I tried to do too many things (age-difference seduction, mind control for starters) and while I know roughly what parts to rip out, I can't get myself to do it yet. Then I've got a 3800 word draft which is solid for about 2800 words then breaks into concepts and mini-scenes that I haven't been able to flesh into a flow.
So I went to my slush pile - a file of about 50 items ranging from six-line ideas to thousand word chunks. And as luck would have it, a story plotted loosely to have eight sections that I hit a wall after the third (five years ago I hit that wall), triggered something in my head and I got a few lines then a few more good writing rush and within a month got all the way to a proper end. So you never really know what draft or fragment may flip a switch and turn on the words.