Replacing them is generally the only way to get it working again
First this is what they look like before they are a rusted blob.
They range in cost between about $30.oo and about $170.00 depending on how large an orifice you require, and if it is a high or low pressure valve. If all that it is supplying gas to is the stove then you could definitely get away with the cheaper of them. However the cheap ones are almost always low pressure valves and are placed AFTER the pressure regulator. This is less than optimal as pressure regulators are one of the first things to fail. I like and it is a recommendation for safety to install a high pressure solenoid valve ahead of the regulator.
If you look at the regulator it has a small hole on the bottom of it. This is to allow the gas to escape should the diaphragm inside fail. This is the most common failure mode for these and does happen with some regularity.
It is unlikely that your hose is plugged with anything, although I have seen people who left the tanks off for an extended period of time have bugs living in the hose and completely plugging it. If you feel that you must blow it out, blow from the stove end out the bottle end.
This is a good time, I would say even a necessity to look at the entire system from start to finish, making sure that everything is in order and that there are no other issues that have occurred in this time of non use.
I like to start at the tank, the simple end and move toward the complex end the stove when I teach about this system.
Bottle, Bottle Hose connection, Gauge, Solenoid Valve (High Pressure), Regulator, Connection to the hose, NO BREAKS AT ALL in the section from the regulator to the stove, stove connection, Burner Feed Manifold, Burner Valves, Burner Air venturi (also called an air shutter), Burner Feed Tubes, Burners, Oven Valve, Oven Thermocouple System, Oven Pilot Light, Oven Feed Tube (I have seen a lot of these with bad holes in them, easy and cheap to replace, but could kill you), Oven venturi, Oven Burner Assembly, Oven Heat Diffusion Plate, Oven Temperature Control Thermostat probe.
Fire away (pun intended) if you have any questions. There is almost a full days class here for most people on how these things work. Most of it is really easy to understand once you have it explained to you. With the exception of stuck safety valves on the newer force 10 stoves is easy to fix yourself.
The first two photos are different photos of solenoid valves, the last photo is of a standard regulator. This is a single stage regulator and is what is found on most boats. There are double stage and adjustable regulators which do a much better job, (Temperature compensated, and anti pulsing), which can be placed in service on boats, but rarely are.