There is no power coming to the fuel pump and nuzzles.I lost my key, but I got another one.I changed the entire key switch.

Do real fuel pressure test using test gauge. You changed ignition module but not coil? Are you getting nice fat blue spark? When spraying starter fluid into intake it only tries to start which makes me think you have ignition problem.

As far as I know a Chevrolet doesn't have an inertia switch like a Ford.
I am assuming you have lost fuel pressure, first thing to check is the fuel pump relay (usually in a fuse box under the hood) make sure you have power to that point (you should hear it clicking when you turn the key on) if you have power chances are you have a bad fuel pump. If you have lost key power to the relay, check the fuel pump relay fuse in the dash for power ( if the fuse is bad replace the fuse and the relay) if no power to the relay fuse you may have a faulty ignition switch, its a common problem with 00-06 Chevy's across the board.

Bad Ignition Switch

Worn out Fuel Pump

Worn Fuel Pump Relay Contacts

Do the proper testing

Do not replace any parts until
they fail a test

If the passkey system were not working the engine should not crank and the fuel injectors would be dead. The security light would also stay on.
The fuel pump relay gets battery voltage and also voltage from the key switch. The computer grounds the relay to power the pump.
The crank sensor does not come into play until the engine is cranking and it supplies a signal for the ignition and injector pulse.
Are you not getting power from the key switch to the relay, or from the battery side to the relay ?

I have no idea what kind of car you have but it sounds like you might have a resistor chip in the key and changing the switch you may not have a key with the chip or a right chip in it.
The theft light being on sounds like it has shut down the fuel pump.
You can have your key resistance checked and put a resistor in the computer to match.
Is yours a Cady?

2003 should be a fuel injected engine. A misfire could cause these symptons mentioned. Check ur spark plugs, if d injectors are part of d problem it could be they clogged ith carbon, service ur injector nuzzles, check n change d fuel filter too. I also advice a look into ur fuel pump working condition, a clogged filter or dirty fuel tank can affect ur fuel pump. Be sure its ok n the pressure s right.

Have you checked the diagnostics with a simple Scanner yet? This sounds like an Oxygen Sensor going or gone bad. The Scanner will tell you. If the Scanner says 'all normal', and the fuel system indicates 'CLOSED' status, check fuel pressure with a fuel pressure gauge. If the fuel system indicates 'OPEN', check the Fuel Safety Switch wiring, inside and out, the Fuel System Relay, and the Fuel Pump. Sorry, but the ethanol in the gas is creating an entirely new class of problems.

change oil presssure switch and fuel pump relay, relay closes when cranking due presence of oil pressure to complete circuit to fuel pump, bad relay or oil pressure switch will cause your problem.

The mechanic should check on the fuel filters , the spray nuzzle and the fuel lines . The fuel filters "the primary and the secondary filters".If these filters are dirty fuel are hard to enter because the dirt keeps on blocking the fuel to pass or go to the engine . The spray nuzzle if it is also dirty then the fuel also is hard to spray or to pass for engine compression. The fuel lines if the fuel lines are worn out or have leak then it should e replaced. These spare parts if they are been worn out or dirty they should be clean or some times be replaced . for good so that fuel will not spill too much on the car.For these problems can cause fuel leaks or engine problems it will result to engine lubrication.

you have a shut off button in the trunk find it turn it off and turn it back on