Final answer:
The first step to troubleshoot the issue of a new hard disk not showing up in a Windows-based computer is to initialize the disk through the disk management console. Afterward, create a new volume, assign a drive letter, and then format the disk.
Step-by-step explanation:
If you have added a new hard disk to your Windows-based computer and it appears as unknown in the disk management console, the first step you need to take is to initialize the disk. This is because before a hard disk can be used, it must be initialized, which creates the necessary data structures for the operating system to read and write data to the disk. After initializing, you will then need to create a partition and format that partition to create a usable volume. Once a new volume has been created, you can assign a drive letter, which will make it visible in File Explorer and allow you to start storing data.