The Stop button is mainly for canceling print jobs and entering maintenance modes. If a job isn't printing, it might not respond. But if you're trying to use it for cleaning functions and nothing's happening, the printer might be in an error state or not fully ready.
First, check the obvious: is there a paper jam? Are the ink cartridges properly installed and not empty? An error condition can make the printer unresponsive to button sequences.
If there's no clear error, try a power cycle. Turn the printer off using the power button, wait 30 seconds, and turn it back on. After it fully initializes (ON lamp steady), try the cleaning sequences again. For print head cleaning, you need to hold Stop until the Alarm lamp flashes two times (for standard) or three times (for deep clean) and then release immediately. Holding too long or not long enough won't trigger it.
If the button seems physically broken or the printer remains totally unresponsive after a power cycle, there could be a hardware fault. That's a service call.