2 things to check:
1. is your Plextor M6S 128Gb connected to first sata on the motherboard?
2. BIOS select Plextor M6S 128Gb as first boot device?
Is your WD Blue 1Tb still connected?
OS in SSD... Able to see SSD in bios but somehow it still won't boot into windows.
the error means the system cant find your OS, there is three possibility
1)the board cant detect your SSD/HDD (board issue, try changing sata ports)
2)Your SSD/HDD with the OS got issue (try connecting the one with OS only)
3)OS corrupted (reformat?)