re: MacBook Pro Flashing folder with ?

Have you tried booting into safe mode. That can remount the HDD, it can take between 20 and 35 Minutes. (It's worked for me before). Also, you can go into CMD+OPTION+R and pull up the terminal and see the bootable drives with "ls -l /dev/disk*" or "diskutil list" to see if the drive is still there.

You can try diagnostics with Apple Hardware Test YMMV

Likely it's the drive.

Source: Worked at the genius bar in college