Still no luck with Xorg, but guess what, thanks to your RTFM bash
, I was able to use hdparm to ATA secure erase my Mac Mini's SSD!
By following the instructions, I noticed that my SSD was in "frozen" state, I tried put my Mac to sleep using the suspend to RAM method, but the monitor wouldn't turn on when my Mac woke up from sleep. So I connected it to my network and did the rest of the job through SSH.
Thanks very much for your help. And if you'd like to know, the graphic chip of my Mac Mini is AMD Radeon HD 6630M, it's the cause of not booting normally, I suppose?