Can you boot into safe mode? From the login screen, before you log in, click the power icon in lower right corner, hold down shift key while clicking on restart. That should boot into the recovery environment and in those menu you can restart in safe mode. In safe mode, if there are no other administrator accounts on the computer, the built-in Administrator account will be available for log in and you can change your user account to administrator or create a new account with administrator privileges.

Really sounds like you are going to have to do a clean install from a Windows 10 install USB/DVD, though. If you use a Macrium Reflect Free rescue disk to save an image of your current installation, you will at least be able to mount that image later to retrieve your data files.