2004 Nissan altama cranks but won't start already changed crank sensors .what could be wrong?

Changing the "crank sensors" isn't going to help, ever. The crankshaft position sensor may set a trouble code due to the engine stall or not starting, but is not often the source of a problem. Diagnostic testing is required to find out if you have a fuel delivery, ignition spark, air intake or emissions controls issue -- or even if you have an engine timing or compression issue. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops