No pressure build up from pump

Looks like this is a small triplex pump.ensure the pump is acually turning over with the power unit and the love joy coupler is working properly and there is no stripped out key ways ect. was the hose jumping before the loss in presure? this could indicate a washed out in the intake or dischage valve. or debris hung up there in. check the pressure relief valve/unloader valve for proper function may be the pressurised water stream from the hose is by passing .repair /replace as required.