Fuel injector or computer box 2000 nissan altima?

I have a hard problem that i can%26#039;t figure out. I changed all the fuel stuff from fuel pump to fuel filter. still doesn%26#039;t start. then i checked the fuel pressure and it%26#039;s a 45 psi which is good. sparks are good. but now i stumbled on the injectors not having power so it won%26#039;t spray the gas into the engine. i checked fuse and wiring and everyting is good would that mean it%26#039;s the computer ECU not sending the signal to the injectors to fire? please help|||Take a look at the cam and crank sensor. If you have a problem there, the computer doesn%26#039;t know to pulse the injectors. If anything replace them both.