Here are your troubleshooting steps.
1. Remove SSD From PC
2. Try connecting drive to another computer. (If you cannot see the drive from the other computer, then the drive has most likely failed.)
3. Attach a different drive to your main computer and see if it is recognized. (If the drive has not failed, then it has something to do with your computer.)
5. If nothing has seemed to be wrong so far during the testing, then possibly try switching to another SATA port on your motherboard.
6. If still nothing seems to be showing any answers, then try switching the cable that supplies power to the drive.
7. If all else fails, disconnect all power from your computer. Remove CMOS battery and wait 10-15 minutes. (If you want, possibly do this first.)
Hope this helps you!
Anthony