I have a Dell E7450. The other day after a restart it went to a black screen and said "No bootable devices found" with options to retry, run setup or onboard diagnostics. I restarted it again and it booted up to Win10 normally. The next day after a restart it gave the same message but this time it has never gone away and I cannot get back into Windows. I went into the BIOS which reported no disk drives

I took out the battery, disconnected and reconnected the mSata drive, held down power button for 30 seconds and tried to start again - same error.

I assumed it was a bad drive, so I bought a Samsung SSD 860 EVO (Sata 3, 2.5" drive). Upon replacing the mSata drive with the new one the BIOS still reported no drive. Popped in a Win10 bootable USB and the Win10 setup did not detect the drive either.

So I hooked the new Samsung SSD to my other laptop via a USB hdd drive cable (connects power and data to the drive and converts to USB) and the drive was recognized by the other laptop. I went ahead and initialized and formatted it to NTFS. Still no joy when I connected the SSD to the Dell E7450.

I upgraded Dell E7450 BIOS to A24 (newest available). Tried Boot Sequence as Legacy and UEFI. Tried SATA Operation as AHCI and RAID on. Secure Boot is disabled. Everything gives the same result - neither Win10 USB setup nor the BIOS detects the SSD. I pulled 2 other drives (1 SATA HDD and 1 other SATA SSD) from my other laptop and popped them in the Dell E7450 and neither was detected. I didn't expect them to work/boot out of the box but the BIOS should have at least noticed there was a drive in I assume.

So what's my next step in troubleshooting?
1. Replace the mSata cable which connects Sata to the motherboard? Seems unlikely that it was this cable that went bad.
2. Get an exact replacement for the mSata SSD the Dell came with - maybe it's just not compatible with other drives.
3. Replace the motherboard. They seem to go for $100 on ebay. Not sure if it's worth it.

Thanks!