Hi,
Thank you for posting your query in Microsoft Community.
It is a state of hard drive where Windows 8 OS files has been corrupted. Once the partition gets RAW then user is incapable to access files \ folders and even cannot be used to store fresh files.
Generally RAW file system issues occur due to inconsistent between several system tables, important file system missing information, severe virus attack, logical glitches, unforeseen issues, etc. In these circumstances different type of error message appears
such as “Drive is not formatted. Do you want to format it now?”, “There was an error accessing drive E”, “The disk in drive E is not formatted”, “File names contain weird characters”, “Sector not found message”, etc. In these situation user is unable to access
the files stored on that partition.
You may refer to the following article to create installation media for Windows 8.1
Create installation media for Windows 8.1
Note: You do require the product key for Windows 8.1 in order to
create installation media.
Once you have the installation made, try the steps below.
a) Insert the installation DVD or USB
and boot Windows 8 from it.
b) In the ‘Windows setup’ page select the language to install’, ‘Time and currency format’ and the ‘keyboard or input method’ and click on ‘next’.
c. Select "Custom" or "Keep nothing" when you are asked to select a type of installation.
Hope this information is helpful. Please feel free to reply in case you face any other issues with Windows in future.