How do I get myself excited about my new story again?

Don't write it for a few days, a week, even a month, but don't stop writing other things. You don't want to lose interest in writing as a whole. In the meantime, think of all sorts of ideas and write them down, doesn't matter what it is. You will eventually find an idea or more that could improve your story, you might even turn your story upside down; improving it.

Sometimes you can't recapture the excitement or bring back the story as you conceived it. I heard or read that Mark Twain stopped writing "Huck Finn" after the steamboat hit the raft, and that when he resumed a while later, and Huck and Jim resurfaced, the story was no longer as lighthearted. That could be just an anecdote. Perhaps Twain did not put the manuscript aside. But an author's perspective can shift a bit when he takes up a story after it's lain dormant.

Re-read what you have written and mull it over for a few hours. If the path is still discernable, go on. If it has shifted, take a point form tour of where it will take you and decide if that's where you want the story to go.

I haven't found diving back into an old story to be that effective (although, sometimes I will read through what I've already written, and get the spark back).

You could try making a playlist of songs that remind you of your story, or make a collage that makes you think of your story in a new, exciting way. But don't push too hard. If the desire to write doesn't come back right away (or overnight), then either start a new story, or just wait and see what happens with the old one.

Sometimes they just die, and there's nothing you can do.