my old sandforce-based fujitsu oem ssd had this issue before, due to my mishandling. i use it with usb-based external enclosure. i did a power recycling with it (meaning, turn a pc off; connect it to power cable only, without sata cable connected. boot the pc; let it run a while. then, turn the pc off again, and unplug the ssd from the pc)

after the power recycling, the oem drive could be accessed properly (data was lost; but i had backups), so i just reformatted it, and gave it a good 15% over-provisioning. that 240gb mlc-based sata ssd is still working fine until today.