Suddenly will not start

This sounds more like an intermittent connection. Chances are it's not a poor battery cable connection because even when the radio and lights start working again, the extremely high current needed by the starter would make them act up right away. More likely there's a loose connection where the smaller positive battery wire bolts to the under-hood fuse box. Also check where the smaller negative wire bolts to the body.

Next time it acts up, try to keep it that way, then use a test light starting right at the battery and work your way down the wires until you find the first point where voltage is missing. That will be the point of the bad connection.