No pressure in boiler tried everything, can u help please?

hello,

Ive been without central heating for 4 days and its freezing, my boiler is 'vokera linea 24' and the water pressure gauge displays '0.5'. When the hot water is turned on the gauge displays '0.3'. I have looked at the manual and it tells me to 'turn the filling inlet valve slowly virtically down to filling position, and u will hear water entering the system boiler' i have done that and i cant seem to hear any water going to the system boiler nor is the pressure gauge moving any further than '0.5'. The manual states the pressure should be between '1.0 and 1.5' so can u help please?