When a new drive is not recognized by Windows 10, and it's known that the drive was formatted before going offline, checking the file system format is crucial. Windows does not natively recognize the ext4 file system, commonly used in Linux environments. If the drive was inadvertently formatted to ext4, Windows would not display or allow access to it. The solution involves reformatting the drive to a file system that Windows recognizes, such as NTFS or FAT32, ensuring the drive becomes visible and accessible within Windows 10.