After several days of trying to get this version to work, I've discovered that if the Help - Tips (for Toolbar buttons) is checked in Options - LibreOffice - General, then LO 3.5.4 becomes unusable. I don't know if I'm the only one with this or why it happens, as the non portable version on my PC at home doesn't suffer from in the same way.
This option was checked in my previous copy of LO Portable 3.5.3 and worked well.
If I've done something wrong or missed something please advise. Thanks.