There is a safety measure on the base of your unit that prevents the cycle from starting without anything loaded into the unit. On a newer unit, the spring may be stiffer and the base unit does not sense that the chamber has been loaded and is ready to begin sterilization.
There are two options you may try:
1. Try pressing down on the chamber to see if this will activate the sensor.
2. Try loading more items in the chamber at a time and running the cycle then.
Over time, the spring will get soft and the issue should resolve on its own.