Story writing. How to come up with a good ORIGINAL story?

Welp, I am kindainto developing a game right now, something I've always dreamedsince I was a kid. I'vestarted building a concept, delimiting the game world, thegame style and all that, but I can'tfind a spark of a good ORIGINAL story. It seems like every time I start something good, there's alreadya similar thing going on some TV show or movie or book or whatever...It's gettingpainful. That keeps me wondering, how do people come up with such great storylines, even when they're sosimplebut catchy? Do they combine and rethinkexisting ideas or they just throw them into an "ideablender" and hope for the best?