engine wont crank can the key transponder be at fault?

my sister turned off the car at work,an hour later she went out to the car and noticed a clicking sound ( possibly starter ) she turned the key off and on several times to stop the clicking. But afterwards the car woundn't start, or turn over. We've tested the starter, battery, checked fuses, relays and changed the ignition switch. I was told it could possibly be the key transponder. If so is there any way to check or test it before I'm forced to take it to the dealer? Do you have any other ideas on what it might be? Thank you....