Hard Drive/OS not recognized after logic board replacement

"I'm suspecting you encrypted your drive so it will only work in your original logic board as its keyed to the S/N of your system. It won't work with the replacement board.

Review this: Use FileVault to encrypt the startup disk on your Mac

You'll need to create a bootable drive so you can enter the recovery key to unlock the drive. If you lost it heres a way to regain it: Obtain FileVault 2 recovery key with administrator account

And if you can't recover it - Ouch! Want to recover a FileVault-encrypted drive without a recovery key? You’re out of luck

While you can undo file vault it will take some time! Your other option is to make a backup (un-encrypted) so you can wipe the drive down and re-install your OS and then recover your backup."

"Hello guys!

Good day...!!

I am using MacBook early 2009 mb5.2

Max version supported by this Machin is Mac os X ek captain. I recently did a clean install of is High Sierra using patch tool. It's working great, except for the hardware of camera and trackpad. And some times I feel very stuck on page. So I decided to downgrade OS. I had contacted Mac customer service, for any assistance. As per the instructions I went to OS recovery and tried reinstal. It always shows me High Sierra. To click to continue download and install. Where I wanted to roll back to the actual OS that came along with it at the time of purchase.

In an another call with apple service care, I followed the instructions internet recovery.

I went to boot menu DiskStation utility and selecting the Macintosh HD and erased all data, and then tried to recovery Mac os. But still the same high Sierra page to download and install. (Atleast it's not download, gives me an error).

And again later, when I restarted I see not HDD recognised or can't get to recovery mode, or boot access, and none of these combination keys working, : Cmd+R; shift+ option+ command+ R; shift+ control+ command +P, press and hold D key while startup, or any are not working.

Except the error of blinking question mark folder. I doubt my hdd dint fail or any hardware components issue. Like above it's mentioned, I believe that after upgrading to High Sierra my Mac logic board had need updated it's files to latest, and now won't recognise hdd, or can't take me to boot. Or recovery.

Need help. Please somebody."

This was very helpful