registry for hardware change every startup

The question is,

in my mac, where i see the registry for hardware change every startup?

Or, in alternative, exist the plist file or the other file where registry change component?

Because i sell imac, and 20 days after, my client complain error kernel panic.

After hardware test, the problem lies in mounted ram.

the problem is that the Rams mounted by me, are different from those that I found inside the PC.

There is a log file that can prove that he has changed in these twenty days?

thank you for the answer