Relax. You just wrote a bunch of sentences in this post. You're fine, you're just a little stuck.
Do you know what happens next in your story? If not, your issue isn't with writing, it's with planning. Try to brainstorm and figure out where you're going. There are a lot of different outlining worksheets on the internet and you could try one of those.
If you know what happens next, do you know what happens after that? Why don't you jump ahead and try to write that scene, and come back to this stuck one later?
Some other ideas - try writing something else. Try a poem, a short story, a descriptive paragraph, or free writing. Just make yourself put words on the page, even if it's "I don't know what to write" fifty times. Let your brain get used to writing again.
Switch up your tools. Do you normally type? Try handwriting, or writing in crayon with pictograms every paragraph, or whatever else will pull you out of your brain.
Try a different location.
Talk to someone about your story and get excited again.
Talk to someone about your characters and remember why you care about them.
Leave this story behind. Just because the story isn't finished doesn't mean you aren't finished with it. Maybe it's time for you to start another story.
Overall? RELAX. The story isn't going anywhere, and it'll be waiting for you when you're ready.