3
Maybe cookies are broken.
Have you tried
http://yoursitename.com/user.php
You site user name, in xoops, is affected by changes only you should make via system admin -> user. You must be logged in as admin to affect those changes.
Unless you have given your web host access to your XOOPS system via "your" XOOPS id and pass they should not be able to change that information.
rocket98