Car won't start on 1996 Chevrolet Lumina

Car won't start. Makes no sound; radio works and lights are bright. Try to start off and on for approx 1/2 hour; car starts after approx 1/2 hour. Runs good for approx 7 days then won't start again; same as before.

Asked by for the 1996 Chevrolet Lumina
It's possible that the starter is starting to fail. You could check to see that there's battery voltage when your assistant turns the key to START while you have a meter or testlight on the smaller START wite at the starter. If there's 12 volts at the START wire and the starter isn't turning, it's defective.
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Yes, this answer was very helpful. I am proceeding to check the starter.