First, give it a full inspection. To do so, turn the machine off and unplug it. Then, check to see if the belt is worn or broken, or if the roller-brush won't move. Also, look for a full bag or any blockage that might be affecting the power of the machine.
Sometimes, new carpet can be a problem because it sheds more fibre and has a tendency to fill bags/bins quickly and clog the air stream.
If everything checks out and your machine still isn't working properly, contact Russell Hobbs Customer Services via our webform here.