My daughters 2003 Ion will occasionally not start first thing in the morning. It turns over for a couple of seconds and then nothing. She can repeat this several times until nothing happens upon turning the key on. After letting the car sit for 20 minutes it will start right up the first time the key is turned. The car recently was rear ended, and the problem show up after tis happened. The battery is in the trunk and was changed. The car was brought in to the mechanic and he couldn’t reproduce this malfunction.
“It turns over for a couple of seconds and then nothing.” For some people turning over means the engine is running under its own power. For others it means the starter is turning the engine, but the engine may not be providing any power. So which is your example.
When it does not, does it make any noise at all? Do lights come on? Do they stay on when you turn the key? Do they dim at any time?
If you turn the key to on, but not start and listen carefully do you hear a slight hum? Have someone stand by the fuel fill point to listen.
It could be a problem with the fuel pump or its wiring as a result of the collision.