I have a Macbook from 2013 which has never had any issues, however it froze recently and upon manual restart I am greeted by a grey folder with a question mark in it. I have tried swapping the HDD for one which I know works and same issue. I am able to boot its hard drive if I connect it via USB and not the internal SATA. Also, I have discovered that if I allow to Mac to reach room temperature completely then it boots fine, so I figured maybe it was overheating and checked the temps after running for awhile and everything seemed normal. The Mac hardware diagnostic also says there were no problems detected after running an extended test. Anyone encounter this before? I am totally baffled.Thanks for the help!