I have a '95 lumina. It died in my driveway and now I have no power to anything including the dash lights. I have replaced the alternater and battery to no avail. What could it be?

Well not being able to see and test the vehicle it leaves me a couple of guess's which you will need to check out.

So you changed the battery ,, ?? was it dead ?? and the alternator ?

check the ground connection leading of the battery terminal to the cars body ensure its connected properly, there should also be a connection to the engine.

check the positive lead wire to the fuse box.

to test this easing (connect a voltage meter a. ground to cars body, b. pos to battery terminal)

if the wiring is fine then the only other possible thing is the MAIN FUSE. this fuse is located in the fuse box and is eighter an 80 amp, 90 amp or 100 amp fuse. open the fuse box and look at where the main battery wire connects you should see the use there. its bolted in place. or simply check the diagram under the fuse box cover.

Other than that its the car battery which you said you replaced and it still didnt work. So again recap
check wiring off battery to cars body, engine and fuse box,
check main fuse.

your problem has to be 1 of the 2 of them.