Have Water but Shower not working

Like everyone over the last few weeks I have had problems with water - problems from no water to dribbling water.

The home is a duplex so I am talking about the top two stories of a three story building.

For the past week I have had water and ample water pressure in the kitchen - so that's on the second story.

On the third story there is the tank and that is filling up. (Or at least I hear it filling back everytime I use water).
The cistern refils aswell.

But the pressure coming from the sink taps and bath taps is very poor. And no water at all seems to be able to make it up the shower hose. And when the taps are on the water pump does not start. (If I turn on the taps in the kitchen I can hear the water pump running.)

Can anyone tell me if the problem might be? I can't understand why there is not enough pressure for the shower even though the tank is full.

could be an airlock in the pipe leading from cistern to shower.

I like to give updates when issues are resolved so here goes (albeit a bit late):

1. There were water issues over Christmas and as part of this the tank emptied completely.
2. Called out plumber and was told that a tank can have dirt at the end of it (not sure why) and this was sucked up when the tank emptied and a grain of dirt got stuck in the motor fan of the pump
3. Plumber removed dirt - and shower worked as normal.