The centre home switch is not working

You can try a reset: Simultaneously hold down the Home and On buttons until the device shuts down. Ignore the off slider if it appears. Once shut down is complete, if it doesn't restart on it own, turn the device back on using the On button. In some cases it also helps to double click the Home button and close all apps BEFORE doing the reset.

However, this could very well be a hardware issue. You may need to take the phone into an apple store or an authorized service center to have it checked.