Symptoms
- Disk Management shows the drive with its correct size
- File Explorer doesn't list the drive at all
- Drive shows as 'unallocated' or with no drive letter
- Problem appeared after plugging in a drive from another computer
Likely causes
- CommonNo drive letter assigned to the partitionWindows can see the partition but won't show it without a letter.
- CommonPartition shows as unallocated spaceThis means there's no usable file system yet, which can happen after certain transfers or wipes.
- PossibleDrive letter conflict with a mapped network driveWindows can silently skip assigning a letter if one is already in use.
- PossiblePartition uses a file system Windows can't read directly (like Linux ext4)Windows shows the space but can't mount it without extra software.
What to do
- Open Disk Management (right-click Start menu, or search 'diskmgmt.msc').
- Find the drive listed by its size and right-click the partition.
- Choose 'Change Drive Letter and Paths' and add a letter if none is assigned.
- If it shows as unallocated and you expect data on it, do not create a new volume yet; check for a backup or recovery option first.
- If it's unallocated and truly blank, right-click and choose 'New Simple Volume' to format and use it.
- If the file system is unreadable (e.g., made on Mac or Linux), install the appropriate driver or use the drive on its native OS.
When to call a pro
If the partition is unallocated and you expected data there, stop before creating a new volume and consult a data recovery professional.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.