I have a 03 nissan xterra have replaced battery, altenator,battery cables. Interior lights and head light don't work and car will not start. Checked the fuses and all are good. What can the issue be?

you have power shorts somewhere. Trace the power wires from the battery positive to the fuse box to the ignition switch and find where power is lost. If none is lost, then trace the ground wires from the battery negative cable on backwards for breaks

Thanks for the info!