It sounds like the inertia switch is probably the problem, so check it first.
If you can push the button on the top down, then it tripped.
Make sure the button is down and then check to see if it will start.
If it doesn't start, put a fuel pressure guage on it and see what the fuel pressure is.
(Harbor freight sells a cheap pressure tester for about $15.00
Fuel pressure should be;
engine off 35-45 psi
engine running 30-40 psi
If it shows fuel pressure then you will need to use a spark checker/tester and see if it is getting spark to the plugs, if it is, then check the compression.
Oh, after re-reading your first post, I should clarify, the fuel pump relay will kick off, once the system sees fuel pressure and will activate again, when the engine is cranked.
Let us know what the fuel pressure is, if it shows spark and what the compression is and we can go from there.