Car will crank but won’t start

Long story short, over the last several
months I’ve put $2,000+ into parts and labor
for my old car, $400+ just in the last 2-3
weeks. Car won’t turn over. Used to if you
pushed the accelerator while trying to start it
but not today. My boyfriend and I have
personally changed the spark plugs and
wires, the knock sensor, camshaft sensor, the
fuel line, the thermostat, and just now the
IAC. We’re at a loss now. Short of replacing
the wire connectors to the IAC and the
battery terminal because it is a bit corroded,
we don’t know how to get this thing started.
Any help would be appreciated.