Question Installing new storage SSD has stopped my OS m.2 drive from booting

May 25, 2021
I have a Sabrent Rocket NVMe 4.0 1TB installed on an Asus Tuf Gaming X570-plus (in m.2 slot 2), and successfully installed Windows 10 on it and have been using it as my boot drive for the last 6 months. This week I took out an old storage SSD and HDD and replaced them with bigger versions, a Samsung 870 QVO 8TB SSD and WD Blue 4TB HDD. I have another storage 480GB SSD installed too. When I went to boot my PC back up, the BIOS no longer recognised the m.2 boot drive. After some troubleshooting, disconnecting all other drives and taking out the motherboard battery and restarting, the BIOS will recognise the m.2 drive in CSM “enabled” mode only, but when it boots I just get “Reboot and Select proper Boot device...” screen. I can see that by going into Asus EZ Flash Utility, and selecting storage to find the BIOS file, it recognises all my Windows folders on the m.2 drive. I just can’t get it to boot Windows. I’m concerned I have some files I haven’t backed up so I don’t want to try a new OS install - if no other option I’ll use a new drive for that. Is there anything in the BIOS that I’m missing? I’ve looked everywhere else for a solution!
check the motherboard user manual for it's M.2 & SATA information.
which M.2 & SATA slots are available may change depending on which are occupied.
also make sure you are using the proper BIOS settings for your drive setup.

try removing all drives and installing the Sabrent M.2 in slot M.2_1.
is Windows able to load?
if so, add the other drives 1 at a time into the proper SATA ports.
if not, than your system partitions may be located on the other drives. in this case i would wipe all system partitions on all drives and start with a fresh OS install.

if you are attempting a fresh OS install,
make sure you remove all other drives except the one the OS will be installed on beforehand.