Network storage is good until it’s not. When access to your files suddenly stops, fixes can sometimes take a long time, especially if it’s due to a failed drive.
Fortunately, this isn’t necessarily the case if you’ve just upgraded from Windows 8.1 (or earlier) to a newer version of Windows. If you encounter an error when trying to access the NAS through your home network, the problem is likely related to the file sharing protocol. Some older NAS devices use Server Message Block v1.0 as their network file sharing protocol, but Microsoft eventually disabled it by default for security reasons in Windows 10. This policy was also carried over to Windows 11.
You can work around this incompatibility in several ways, depending on the manufacturer of your NAS. The most ideal option is to apply a software update that includes support for SMB v2 or higher, but not all vendors have added this support. If so, you can try enabling NFS, an alternative protocol, both in your NAS’s management interface and in Windows.
If none of these solutions work, as a last resort you can re-enable SMB v1 support, but you will also expose your computer to noticeable security risks. (You can read more about them in this clear and passionate explanation of these risks from a Microsoft employee.) SMB v1 is deprecated and weak enough against threats in Windows 11, Microsoft is in the process of completely ending support. If you really need SMB v1, you will have to find and install the files manually.
If you find yourself in a position where only SMB v1 will work and you care about security, unfortunately your best bet is to upgrade your NAS and invest time in this data migration. But hopefully you’re not in that boat and can instead focus your energies on the neat things you can do on your new version of Windows.