Do you have a good local wifi signal that you have the password for? (I know, stupid question. Some people don't think of it.)
What happens when you enable wifi? Does it find any signals?
Are you trying to connect to a signal with the same name as one you've connected to in the past? (If that's so, "forget" that connection and connect again. Android can only remember security requirements on one signal of a given name.)
Oh - has it ever connected to a wifi signal? The wifi radio could be bad out of the box.