rather than the logic board.

The flashing question mark, the missing disk under the startup manager and the rebooting several times before success, all point toward a drive problem.

Get the data backed up ASAP and consider your options.

1. Clean install of the OS
2. Archive and Install of the OS
3. Replace the drive

I would go with #2 first but I would also contact Apple, under the AppleCard, to start the ball rollling on a replacement drive.

Let us know how you get on