sounds as tho you may have a kill switch wired to your fuel pump.
i had a 90 si at one time, rebuilt its head and never saw a "switch" under the hood soooo...
do u get dash lights when ignition is on? (i assume yes since it cranks)
if so...remove the 4 spark plug wires and insert a screwdriver into the plug wire tubes. hold the screwdriver about 1 inch or less from the valve cover and check for spark on each cylinder while someone cranks the engine for a few seconds each time. also try smelling the muffler while someone cold cranks the car...if you smell noticable gasoline then you are not getting spark.
if you dont smell any gas than its probably the fuel system.
does the car just not start or were you driving it when this happened?
if u answer those questions we can go from there
~boom