95 Nissan Altima GXE wont start, already checked fuel pump,fuses,top fuel filter. tested fuel pump with light tester and it stayed on for 3 seconds then off. what else can i check? I hope it isnt the ECM anyone have any other ideas what i can check please

verify ignition/spark/timing

Any codes?

check for a spark at one of the spark plug wires/coils.
If spark exsists, check timing belt; make sure the camshaft turns when the engine is cranked over.
Next align timing marks to be sure camshaft ans crankshaft are in sync.

check autozone for proper timing mark alignments.

Try www.autozone.com for the step-by step guide along with pictures for this procedure.
Once at the site identify you car under the heading "current Vehicle"
Next click "Repair Info" on the tabs below the AutoZone logo.
At the middle of the page go to "Your Ride, Your Guide" and click "Become a member" set you username and password
Log-in and click "Vehicle repair guide"
Select the category for the repair needed.
Select (on the left) type of repair needed.
Page opens to your repair info.

be sure that fuel is getting to the cylinders by spraying some carb. cleaner into the intake manifold and then trying to stat the engine.

or by using a testlightt to check for power at the injectors. light should flash as the engine spins over.

In addition to what has already been posted, you shouldn't overlook compression problems and excessive exhaust back pressure problems.

if it is getting a spark you could check timing as suggested in an eariler post (basic step included).
If the engine spins over as normal, I would also check fuel pressure (using a fuel pressure guage). There have been instances where the pump could be heard running but it didn't produce enough pressure for the engine to start.

THANKS TO ALL WHO REPLIED TO MY AUTO PROBLEM. I WILL LOOK INTO ALL YOU HAVE ADVISED. I WILL LET U KNOW WHAT THE OUT COME IS. AGAIN THANK YOU AND GOD BLESS ALL.

You're Welcome.

Thanks and you're welcome. We'll be here when you need us.

Remember that te ECM would be the last thin to replace. You have to verify that the other components are good first.