2005 Hyundai sonata V6 seems like a security problem; out of nowhere it can refuse to start, dash lights come on everything normal but ignition is dead. After a period, it starts normally; on occasion the 4way flashers have come on when it was having a no start problem; Any ideas?

I agree with your analysis--security system problem. Best to take it to the dealer. Another possibility is an intermittent Crankshaft Position Sensor or Camshaft Position Sensor failure. Frequently, but not always, a code will be thrown.