There isn't enough info here to give you a solid answer, but from what you have said I think you might find the issue was never the fuel pump or the ECU but something else entirely.
Typically there is only one broken part in electronics that make lots of systems experience problems.
My best suggestion is put all the original parts back possibly even the fuel pump and see if there is something else like a malfunctioning security system or engine kill switch.
Information I would need to give you a better one would be:
-- make model year of car
-- aftermarket upgrades especially sound, security systems, and performance sensors and firmware
-- why did you change the fuel pump? Was it a gut feeling? was it because someone said to do it? was it because you told the mechanic "change the pump" without having them diagnose the problem? was it through exhaustive diagnostics including powering it up manually with direct 12v power if possible and checking to see if it was even getting proper power?
-- same questions about the computer?