This has happened two months ago and was fixed, so I know the drive isn't dead. But I resolved the problem by using Safe Boot Mode (hold Shift at boot) and then repairing the OS X structures in Disk Utility. Now, Safe Boot Mode doesn't work. It just skips right to the blinking ? icon. Running the OS X Install Disc, Disk Utility won't find the startup disk. Resetting PRAM did nothing but make the loud boot chime come back. How it happened: Startup disk (Macintosh HD) was running low on space. I went to the Fast User Switching (Login) screen (did not log out) and came back and the Mac was stuck with beach ball mouse pointer, crashed. Powered off then when turned back on, blinking ? mark icon. I presume something went corrupt because of the low space and it not being able to resume from Fast User Switching. I am unsure if the drive is failing, or if I made something become corrupt by running the startup disk to almost nothing (under 1 GB remaining) while trying to resume. What are my options to get everything back to normal, or at the very least get my data? I have read about tools like Disk Warrior but people with this problem have said nothing gets listed in that just like nothing is coming up in Disk Utility for me. I have tried reconnecting the RAM sticks and even in different slots and no luck. Have not tried reconnecting the SSD cable connections but there is no way that just all of a sudden went loose. It seems tightly in the slot. Can the SSD be placed in an external enclosure and connecting to another computer (Mac only?) and I can view and back up the data as if it's an external drive? This may be more difficult than usual because the drive is a PCi-e drive (https://eshop.macsales.com/shop/SSD/PCIe/OWC/Mercury_Accelsior/RAID). I bought the Mac Pro used with this inside of it (most other components were replaced with new ones though). Is Target Disk Mode the only way to see these files if you can't put that in an external enclosure/bay (have not tried yet). If I am able to put that in an external enclosure/bay, will there be permission problems to see the drive's contents? I do not really want to have to install a fresh OS X, redo all of OS X's settings and app settings but if my only choice is to get the data and reinstall to a new SSD then that will have to be. I have no Time Machine backup.