I just tried activating plugins in your admin, and it worked fine! can you send me a screenshot of what you mean ?
And regarding the other plugins that you don’t know, we recommend deleting them through the ftp, because I am not quite sure what they are, but they might be viruses.
Because they were active, and not appearing in the plugins page, we had to use WordPress
get_option('active_plugins') to see that they were active.