What caused this to happen?
 

I have a 2008 HHR SS with just a little over 80,000 Km (50,000 miles) on it. Yesterday, I parked somewhere, locked the car as I normally do with the remote and went inside a place of business for maybe 30 - 40 minutes. When I came out and tried to start the car it would not turn over, No cranking at all. The battery is new and had plenty of power and all the accessories worked. When I tried to start the car it acted exactly like the clutch pedal wasn't pushed in. The computer wasn't letting the power get to the starter so nothing happened (no cranking) when I turned the key.

Because the car acted the exact same way whether I had the clutch pedal in or not I reasoned that maybe the clutch position switch had just suddenly failed without giving any prior indication that it was about to crap out. I called the closest parts store which was only a few blocks away from where my car was and they told me a replacement switch would only cost about $14 and they could have ione tomorrow morning (today) so I said to go ahead and order it.

I noticed that whenever I turned the key all the way to the start (crank) position and the starter wasn't engaging, the only warning lights showing on the dash panel were the check engine light and the security lock (the padlock through a car symbol). Don't lnow if that means anything or not. Previous to this happening, the car was not flashing any indicator lights. Everything was normal.

Considering there's only one little screw holding those clutch switches in, they sure are a PITA to remove and even a bigger PITA to install.

Anyways, I got the new switch installed but nothing changed when I tried starting the car. Still no cranking. Same indicator lights appearing while cranking. I thought for a minute and finally decided to disconnect the battery for a few minutes to see if resetting the computer would help. It did. It fixed the problem. The car cranked and started right away. Joy! :guitar:

I'm super happy at the outcome but at the same time I'm very curious to know what caused the caomputer to all oif a sudden not let the engine crank. It doesn't seen like the clutch position switch was the problem after all because replacing it with a new one didn't fix the probem. Resetting the computer did.

Can anybody hazard a guess as to what the cause of the problem was and why the car suddenly refused to even try to start?

You should have pulled the codes before you did the battery disconnect. There may have been a trouble code stored that could have pointed you to the actual problem.
Since disconnecting the battery erased any codes, it could have been any number of things that caused the no start. You may have to wait till it strands you again so you can check for those codes.
Not blaming you for trying the battery disconnect. I'm sure you just wanted the car to start.

Might have been a ghost in the security module. My Dad had that on his Impala, and the tech tried the same thing you did and it never came back - after ordering the security module in the Steering Column.

In the past, IF it's the clutch switch, I have had some success with partial lifts off the floor with the key in the start position - in other cars. It seemed to clear something up when I wiggled the pedal. I don't know why it worked.

Glad you got yours figured out, at least for now.

Could have been a loose battery terminal.

There were no indicators before I stopped in this parking lot so I didn't erase any codes. Battery terminals were both very tight and uncorroded. I like the ghost theory. effing computers!

Loose ECM connection or fuse or relay.
Or paranormal activity! It is a full moon!!

Just because you didn't have any "indicators", (CEL) there could have still been code(s) stored in the computer. Not all trouble codes instantly turn on the CEL.
Saying "I didn't erase any codes" is not necessarily true. If you did the battery disconnect like you stated, it reboots the computers and clears any trouble codes ,seen or not.

The only codes that set the CEL are the EPA related codes. There are lots of codes that point to electrical problems, for instance there are 2 codes relating to the ambient air temperature sensor.

I see. That's unfortunate because I had a code reader in the car and could easily have checked. I actually thought about it but then (mistakenly) thought there wouldn't be any codes so I just disconnected the battery and (hopefully) solved the problem,