If your proposal has been rejected by the funding agency, don't worry. It certainly doesn't mean the proposal's worthless. Ask for a reviewer's report. This should give you valuable insight into why the proposal was rejected and what you can do to revise and resubmit it. Sometimes the smallest problems can lead to a rejection, other times you could just be "fighting the numbers." Find out what went wrong, it can make for a stronger proposal next time around.

Sometimes a proposal has simply too many errors to resubmit. This isn't uncommon and most experienced grant writers have a rather large collection of abandonded proposals. Take a look at your original idea, is it something that can be used in another grant, or could another faculty member use the information you've gathered. Nearly all proposals can be recycled into something useable. So check it out.