Z34 cranks but won't start!

Hello everyone,

I'm normally good fixing cars, but I am a bit lost with this problem:

It's a 92 Lumina Z34, 150k miles
The car was working fine, I parked it, fixed one headlight assembly, and now it won't start.
It cranks fine, everything works, full battery, AC blower, windows, locks, turning signals, back up light, brake light, wipers, radio, fuel pump, BUT NOT the headlights, which were working before.
It is unlikely that I damged anything, I just took the headlight assembly off the car to fix the height alignment screw, then put it back in the car
The other thing I did yesterday was replacing the strut carttridge in the right wheel, but after that the car was OK to go shopping.

I don't understand what could the connection between the engine and the headlights be, and it can't be a coincidence that they failed at the same time.

A theory I have is that there might be an alarm system with an immobilizer, there is a valet button and I hear funny beeps and chirps when I press and hold it for a few seconds. I got the car with keys only, no remote, so after I finish this post I'm digging under the dash to find that alarm system. Then again, why would it lock the engine by itself?

I checked the fuses in the right electric panel, ECM, ignition, fuel pump and they are all good.

If I switch the ignition on and off 5 times I get some flashing of the dashboard lights, is that normal?

Well, I have been getting lots of useful information in this forum since I got the car, I hope that you can save me once again!

Thanks a lot,

Nestor


Las minute update: I just went to check the car and everything works! I still need some help though, as I am going on a road trip with my girlfriend and I don't want to be stranded in the middle of nowhere. When I bough the car the headlights didn;t work, and thanks to that I knocked $200 off the price, then by miracle they worked the next time I started the car. What could it be?
I'll still dig for the alarm system, I guess that by knowing the make and model I should be able to get a remote?

Could have some loose wires. Might be hard to find.

Sounds like a major grounding spot may be bad???

Get a pair of booster cables and run it to the starter from a battery, with the ignition on, if it starts check wires to starter, and go from there.

Thanks, but the starter works fine. I thought about directly energising the ECM or something like that, but I guess it could really screw things up.
The other cars I have are a 1978 Jeep and a 1975 Hurst/Olds, I always know what is wrong with them, now I am starting to hate computers :)

the car seems to have fixed itself, but I don't believe in miracles, I know it's going to happen again...

my Lumina is the eaxct same color as your by the way, bright red.

srry dont know why i wrote that

your ECM is in the passenger front fenderwell, directly behind the headlamp. It is very possible that you have some corroded terminals at the ECM that you tugged on/bumped/disturbed when removing the headlamp assembly.

The only thing i can think of that is fine one day and gone the next is the crank sensor. If it went bad it will not start.
Just my thoughts on this.