Please help I replaced the starter , battery, ignition switch, in a 2000 mazda protege dx manual the dash lights up but when I try to start the car nothing happens ! Any answers ?

The starter pulls a lot of current. Make sure your body/chassis to engine grounds are corrosion free. Aside from that, check to see that the main power fuse end are not corroded as well and that the starter relay is operating. I'd remove the fuse and clean, possibly replace it. They get old and worn out too.

I had a similar issue, try the main 100 amp fuse. mine was bad. I ended up replacing the battery with a bad cell, the alternator because it was bad, and then also the main fuse.