Alpha Ocean 240E Boiler not working?

Hi

Sry for asking amateur style question as I completely dont know about Boiler.

I have just moved into a house. Yesterday I turned the boiler off. Before turning off everything was working fine - hot water and central heating system and the pressure gauge showed near green area which i think is between 1 - 1.5. But when i turned it back on nothing was working, I could hear some waterflow noise from the boiler but the pressure gauge was down to zero and it turned up.

Can you please help me with the problem.

Many thanks in advance..