MacBook Pro (2011) shows flashing folder at startup but the disk is valid I have a MacBook Pro (early 2011) and recently the laptop boots to a white screen that flashes a folder with a question mark. I know that means the laptop cannot detect an available startup disk.

I confirmed the disk is valid by removing it from the laptop and connecting it externally to another MacBook Pro and it's immediately detected and I can browse the file system.

On the faulty MBP I have:


Booted in to the recovery console (Cmd+R at startup) and Disk Utility does not even detect the internal hard drive. 
Cleared the CMOS (I think that's what it's called) by holding Option/Cmd/R/S at startup for three consecutive reboots.
Removed the harddrive and reseated the connections to the drive itself as well as the logic board.


I am out of ideas on how to resolve or continue troubleshooting so please let me know if there is anything else I can check or how to pivot? My next action would be to make a Genius Bar appointment because I'm worried to logic board is somehow faulting.

edit: I tried another test with mixed results. I swapped the hard drive cable from my functioning MBP in to the faulty MBP and the laptop booted successfully. However, a few moments after login the screen switched to white with the flashing folder/question mark.

I moved the faulty hard drive cable in to the functioning MBP and the laptop failed to boot successfully.

My signs are kind of pointing towards a faulty hard drive cable. $45 for a replacement on iFixit seems kind of steep...
The problem was a faulty hard drive connector cable. I ordered a replacement from iFixIt and the laptop is functioning again.