No one has answered? OK. Power off the computer. If you have a power supply that has a switch, shut it off. Hold down the power button for 10 seconds. Open the case, unplug the SSD cables to the board and drive. Replug, turn the power supply on. Fire up the computer. Check if BIOS sees the drive. It's all I can think of, good luck.
Hi Saladin, if re-seating the SSD does not bring it back then it might be a good idea to test the SSD in a different system, since it may mean that the SSD has failed.
If it does come back then the next step would be to verify in the event viewer to find out what caused the shutdown of the computer,
(Click on start, in the search box type ‘Event viewer’ click on ‘Windows logs’ then on ‘application’ and ‘System’ check for both options in the middle pane to see if any entries apply to the date and time the shutdown occurred.)