When you turn your key to the on position, your check engine light should come on for a couple of seconds and go off. At this same time, your should hear your fuel pump go on (prime itself) under your back seat. Do you hear it?

If your main relay is faulty, it will be intermitent. Having it checked will not always show it not working.

It wouldn't smell burnt because the problem is with dry solder joints on the relay that expand and contract based on the temp.

Just replace the relay, or fix it with the links above.