Why won't files in my onedrive open anymore?

Thanks for reporting this. The brown box icon means the files are online only and OneDrive sync is not fully active.

Please check the OneDrive cloud icon in the system tray and confirm your account shows “Up to date.” If sync shows paused or signed out, sign in again with the same Microsoft account. Once sync resumes, right click one file and select “Always keep on this device” to download a local copy and test opening it.