(sorry for the bad english !)

Hello,
The car stalled at an intersection a few days ago, all the lights turned on, I was surprised as it was the first time an automatic car stalled in my hands !
I was unable to restart the car even if the starter would turn, but the engine wouldn't fire up. It just turned for 4 seconds, then stopped. I tried a few times, then decided to park it.
I remembered reading something about a faulty weld in the engine control box so I told myself it was the problem, but when I came home (by foot) it appeared that if the weld was the problem, the starter won't even turn the engine, just as if the car was dead.

So it appears to me that I have 2 possible problems, a Camshaft PS problem, or a Crankshaft PS problem.
Can I possibly know wich one it is ? As I do not have an OBD reader.

And, if I buy a OBD reader, will it tell me what is going on, as when I restarted the car, 6 hours later, the engine problem light didn't come on ?

Thank you..