ultimate-branding error on custom coding: (WP) interface dissapears

I made an error in the configuration of the Help-section.

Where I put:

    <li style: list-style-type:none;>

    Should have been:
    <ul style: list-style-type:none;>

  • Now all the pages of WP show up blank ... no content at all .....

    Menu still visible and working, but no content is generated, this is for ALL links .....

    I managed to remove the plug via FTP.

    But reinstalling the plug generates the same situation .....
    So there must be some remains, somewhere.

    Any tips on how to:
    A. Really reset all settings?
    B. And/ or reinstall the plug?

    Thanks in advance.