My 2003 ols Alero turns over and wont start. Sometimes it does. Crank trigger has been changed as well as fuel modulator. Back at the shop without a clue.

Sounds like the computer is dead, or not getting a signal from the crank sensor.
Can you check the crank sensor with a meter, or use a scanner to check data input to the computer ?

It might be the starter or solenoid going bad.

Could be several things or even more than one problem. First, determine if this is an ignition issue. When it won't start and the ignition is ON, does the instrument panel light up, i.e is the ignition circuit coming on? If not work to solve ignition issue, ignition switch, etc.
If the ignition comes ON but it won't start, do you hear or did you hear the electric fuel pump run for a few seconds? If not, work on fuel pump circuit. Don't assume a bad fuel pump, as the wiring is often the problem.

the fuel pump is the part that fails most not the control module or relay.

I was reading another comment about Aleros and thought you might try this. You have an antitheft system that kills the fuel pump. The directions are in your owners manual. What I remember is to turn on the ignition and leave it on for 10 minutes. Now whether you turn the car to start at this point or go back to "off" and then start is the second way. I would try turning the key to start without shutting it off (from the 10 minute cycle). This is suppose to reset the antitheft and you should observe whether the antitheft light is blinking.

If this works for you then you have problems in the antitheft circuit. This would include keys, keyswitch reader, connecting wires and antitheft box. Best of Luck

First, look for broken or loose wires in the ignition circuit, and the coil wires. Then try fuel filter. Then, ignition module, coil, and timing. It could also be dirty or clogged injectors.

try locking and unlocking the drivers door with the key. [sometimes if you reach to un lock door through window it it sets off security]

Hard to determine without a diagnostics test. Since you replaced modulator and fuel pump and have same probelms, I was wondering:
Does it not fire or not turn over at all?

If you are not getting power to fuel pump at all times, that it may be a fualty Computer which can be about $400 to repair. VERY COMMON PROBLEM WITH GMs.

Do you have any engine codes? Or is your check engine light on?

Have you checked all your relays? This is the first thing I would do. You can check them with a digital ohmmeter or voltmeter.

youve either got a weak fuel pump,or bad pressure regulator,or clogged fuel filter change it first!!!

Check to make sure the Security light in dash on right hand corner is not on. If it is on , your passlock is enabled. to dissable it turn your key on but not start it and wait for apx 10-15 minutes. this should re-set it.