Hello you can go into the bios and load defaults. It usually solves this problems. What memory did you installed ?? Memory it´s very picky in this systems, the problem can be related to the memory also. Regards.
I installed some additional memory in my Area-51 R5 and now it no longer boots from the M.2 PCIe SSD. The device appears in the BIOS but I get: "Internal hard disk not found to resolve this issue, try to reseat the drive. No bootable devices" reported by SupportAssist. Now when I installed the memory I did a Restore Defaults in the BIOS and so it is possible that I have cleared a setting that the M.2 needs. So my question is are there any changes I need to make to in the BIOS for it to pick up the M.2 once more.
Area-51 R5 BIOS Settings for M.2 PCIe SSD-1