Windows Won't Load When I Install Second NVMe SSD, How to Fix

Hi everyone, I have a problem, and I need some help. I have an Asus Pro NVME M.2 SSD as a Windows drive. Everything works fine with the default BIOS settings. I bought a second NVWE M.2 SSD, and if I install it, the BIOS won't see any boot devices in the list, even though in the M.2 list, it sees two drives. After I activate CSM support and reboot, the boot drive appears, but even though I select the correct boot drive, I get the message to reboot and select the correct boot drive. What should I do?

Reasons for restarting and choosing the correct boot device error are various, for example, MBR corruption, incorrect boot sequence, boot file corruption, partition not set as active, hardware failure, etc. Next, I will share some of my experiences to help you. These ways work well on this issue:

Fix 1. Check the Boot Order in BIOS

This guide will teach you to set the correct boot drive:

Step 1. Restart the PC and press F2/F12/Del key to enter BIOS.

Step 2. Go to boot options, change the boot order, and set the operating system to boot from the new SSD. Remember to save your changes promptly.

Fix 2. Set the Correct Partition as Active

The partition holding the Windows boot files should be a very active partition. Otherwise, Windows will not start. Here, I recommend you use third-party software. Based on my tests, EaseUS Partition Master can set a partition as active with simple clicks.

Here is how:

Step 1. Run EaseUS Partition Manager software. On the disk map, right-click the target partition and select Advanced.

Step 2. Then, choose "Set as Active." Click Yes. Then select Execute 1 Task and click Apply.

You can also use this tool to rebuild MBR to fix this error. Follow Fix 3 to continue.

Fix 3. Rebuild MBR

It might be a little difficult, so I recommend you click the link below if you want to learn the details of how to rebuild MBR for your NVMe SSD: