If you've repeatedly attempted sourdough starters with dismal results, it could be that, depending on where you live, the wild strains of yeast floating in the air may not be well suited to sourdough. You can easily overcome this hurdle by purchasing a dried commercial starter for a minimal fee. Cared for properly, your starter should last for many, many years. If you have other ferments or cultures in your kitchen, keep your starter at least several feet away from them to prevent cross-contamination.