How do you know is the solenoid, could be the pump or the restricter is block.
Which machine do have?
What is the problem?
The solenoid is divided in two parts, electrical and mechanic. Enclose more information how machine works.
The Basic Layout Of an Espresso machine with a 3-Way Valve
http://home.surewest.net/frcn/Coffee/3way/1.html the enclosed website has a lot of useful information .
Di Bartoli Home Barista centre