There could one of several reasons. 1. It could be there is no water in the tank. Obvious but be sure you’re filled up. While you’re at it, make sure the tank is pressed down all the way so water can flow into the machine through the valve. 2. The holes in your filter holder are blocked. In this case take a pin to clean it out. 3. You may need to clean the espresso boiler, because it could be blocked. 4. It’s time to descale your machine.