I need to purge my plumbing as its to noisey, the tap that I fit the hose on to let the water out is not letting water through, I have turned the valve to open, turned off the feed and kept power to the system, what am I doing wrong

We need more info, what " kept power to the system" ? Is this on a well? Or are you trying to drain or flush your water heater?

More details please!~ Your post is confusing to us. Can you be more specific? Back to you, Tom