If you purchased a new computer and upon first boot up, you notice that one or more of your hard disk drives is not showing up, there is a small chance that it has lost it's initialisation prior to shipping. This could be caused by last minute changes to the order involving hardware changes such as incompatibility or other issues. 

To solve this, you will need to initialise the drives that are not showing up. Follow the instructions below which will guide you on how to initialise, partition and format your drive to make it usable.

Initialise new disks

If you add a brand new disk to your PC and it doesn't show up in File Explorer, you might need to add a drive letter, or initialise it before using it. You can only initialise a drive that's not yet formatted. Initialising a disk erases everything on it and prepares it for use by Windows, after which you can format it and then store files on it.

To initialise new disks

Here's how to initialise a new disk using Disk Management.

1. Open Disk Management with administrator permissions. 
   To do so, in the search box on the taskbar, type Disk Management, select and hold (or right-click) Disk Management, then select Run as administrator > Yes. If you can't open it as an administrator, type Computer Management instead, and then go to Storage > Disk Management.

2. In Disk Management, right-click the disk you want to initialise, and then click Initialise Disk (shown here). If the disk is listed as Offline, first right-click it and select Online.
   Note that some USB drives don't have the option to be initialised, they just get formatted and a drive letter.

   

3. In the Initialise Disk dialog box (shown here), check to make sure that the correct disk is selected and then click OK to accept the default partition style. If you need to change the partition style (GPT or MBR) see the Microsoft Windows guide About partition style - GPT and MBR.
   The disk status briefly changes to Initialising and then to the Online status. If initialising fails for some reason, see the Microsoft Windows guide A disk's status is Not Initialized or the disk is missing entirely.

   

About partition styles - GPT and MBR

Disks can be divided up into multiple chunks called partitions. Each partition - even if you have only one - has to have a partition style - GPT or MBR. Windows uses the partition style to understand how to access the data on the disk.

As fascinating as this probably isn't, the bottom line is that these days, you don't usually have to worry about partition style - Windows automatically uses the appropriate disk type.

Most PCs use the GUID Partition Table (GPT) disk type for hard drives and SSDs. GPT is more robust and allows for volumes bigger than 2 TB. The older Master Boot Record (MBR) disk type is used by 32-bit PCs, older PCs, and removable drives such as memory cards.

To convert a disk from MBR to GPT or vice versa, you first have to delete all volumes from the disk, erasing everything on the disk. For more info, see the Microsoft Guide Convert an MBR disk into a GPT disk, or Convert a GPT disk into an MBR disk.