When my 2004 santa fe sets for 20 hrs or more it sometimes won't start. It gets full power all light work, it just will not start, i trun the key off and wait 30 seconds and it might start or i will have to do this again, never more then 3 times. Once it starts I have no problems with it.

This is caused by a worn starter, a test can be done when its acting up, all you need is a test light and test for power to the small wire on the starter while someone hold the key in the crank postion if that wire has power then the starter is bad,this is very common it will get to a point where it wont start at all it will start taking longer and longer to start. replace the starter. hope this helps.