2002 Chevrolet Impala - Intermittent won't crank with key in start position.?

When this happens it seems to go dead electrically. When I let go of the key and it goes back to the on position everything electrical seems to work fine. Then I will try to crank it again and nothing, no clicking under the hood, starter does not crank. I have put a test light at the starter and it is not getting power when this happens. Usually I wait about 10 - 20 minutes and it will start. Then it usually doesn't happen again for a month or so. Anyone with similar problem or sugestions?