I don’t think TI can do a backup of itself at the moment, but depending on your hosting provider they probably provide it as a service. If you’re looking for a more hands-on approach then you can also just back up your database with
We’re gonna need some more info to help out on the system error - paste up the errors you get and any output in the system log so we can try to help.
Lastly you can’t remove the links from the user admin menu, but if you really need to then it looks like the file you’re looking for is
app/admin/views/_partials/top_nav_user_menu.blade.php. I strongly suggest you leave that as-is though!