There are several things you should check to figure out what is keeping your machine from producing espresso.

Start by simply making sure your reservoir has water in it. If you are using a tank-less machine, which receives water straight from your water system, make sure the water is turned on. When using a machine with a boiler, you may just need to prime the pump, to put water into the boiler.

The coffee, itself, could be blocking the water from making it through. This is caused by having too much coffee in the filter, or using coffee that is ground so finely the density does not allow for water flow, or tamping that is too firm.

The pump may be clogged, altogether. Descaling is a process that should be done about once a month, but if you are not able to get espresso to come out of your machine, you may want to try running through a descaling process. This will clear any mineral deposits that could be stuck in the pump.

One last thing to check is the screen inside the group head. Coffee can build up on this screen, so remove it, by unscrewing the screw, and give it a thorough cleaning.