There are different actions you can apply in situations where the drive is not bootable, and some details required in order to identify possible causes for this issue.
- Check if the information of the SSD is shown normally in the BIOS (model, size, etc).
- Confirm that the SSD is set as the first boot device in the PC BIOS.
- Connect the SSD using different cables and SATA port, then check if the issue is solved.
- Connect the SSD to a different computer as a secondary drive, using different cables, and check if the data can be accessed from a different computer.
Please try these actions and let us know the results. For further recommendations provide answers to the following questions, was the SSD working fine before? where there any changes made to the system? did you notice any issues before the situation started? what error or warnings do you receive in the system?