Take the supply fuel lines off as they go into the selector valve one at a time and point them into a bucket. Have someone turn on and off the key a few times and see if the fuel line is pumping out fuel. It should also have about 6psi fuel pressure at that point.

If they both put out fuel then take the fuel line off going into the high pressure pump and point it in a bucket. Do the same thing with the key. If you have fuel coming out of that hose then do the same thing with the fuel line going into the fuel filter.
Note that the line going into the fuel filter will be high pressure fuel up to 95psi into a blocked head.