Chosen Solution
there is a folder icon with question mark when starup, I tried recovery mode. and there is no partition or hard disk detected. I also boot the computer from a portable hard drive, still no disk detected. I did some research, except changing whole logic board, they said change I/O board may solve the issue. Is this worth to try？ thanks
Hold down the option key when booting from your external drive. Let us know your results.
