1. Open the Windows search function by pressing the 'Windows' key and the 'F' key on your keyboard simultaneously.
2. Type 'proof.msi' (without quotes) into the search field and press 'Enter.' You may need to use the 'Advanced Search' option to search everywhere instead of the traditional indexed locations.

3. Write down the location of the file once it has been located. The path should look something like this: C:\MSOCache\All Users\{90120000-002C-0409-0000-0000000FF1CE}-C\Proof.en
4. Run the Microsoft Office installation wizard again. When the proof.cab error appears, go to the input field at the bottom of the error message and remove the 'proofing.en-us\proof.en\proof.msi' from the file location using the 'Backspace' key.
5. Type the file location that you wrote down in Step 3 into the box at the bottom of the error message (this is the input field that you cleared in the preceding step). Press 'Enter' to complete the installation.