Originally Posted by
goldenband
That sounds like you could have the well-known overheating problem. Is it an original-model Intellivision, i.e. not an Intellivision II, III, Sears, or Super Pro model? If so, then quite a few of them suffer from this, unfortunately, and I'm not aware of a straightforward fix though a repair is possible.
Of course this assumes you've cleaned the contacts on all your games with isopropyl alcohol, etc., but they probably wouldn't boot to begin with if that were an issue.