Why can't I think of any original music? Specifically the melody?

I wrote some lyrics, but for the life of me I can't think of ANY music! I can't just start to "plunk away" at a piano, sadly, I don't play instruments. And nothing is magically coming to me, I wrote the lyrics almost a year ago! I know the genre is pop, and i want it to be a fast paced song. I just really want to get the melody, this is driving me nuts! I think if I get the melody, I'll be fine and can figure out the rest on my own. How do I get inspiration and how do I figure out the melody for my lyrics?