1. When Command Prompt starts, run net user administrator /active: yes command. By doing so you’ll unlock the administrator account.
2. Now log off of your account and switch to the newly enabled Administrator account. From there you should be able to access your files without any problems.
3. After you’re done using the Administrator account, go back to your main account and start Command Prompt as administrator again. Now enter net user administrator /active: no to disable the Administrator account.

Keep in mind that after switching back to your main account the issue might still persist. If needed, you can use the Administrator account to make the necessary changes to your system and fix the problem.