okclarkkent
You say the battery is charged, does this mean the starter motor is turning the motor over, and the car is not starting?
If the answer to the above question is yes (1 day it worked fine and the next it didn't), the it is not an interlock problem.
But if the answer is NO (car not even turning over) then there may be an interlock not happy that we could help talk you through.
Let us know
ASM