No remote connection works

Don’t really know what’s happening, and need some fresh ideas to keep working; I’m stuck.
I’m currently updating a worpress site; I’ve downloaded it to local server, updated wordpress and plugins, created a child theme, uploaded it again. Everything seemed OK.
The site runs good, but I am unable to get any youtube or flikr plugin run. I’ve double, triple and cuadruple-checked all the user settings on every plugin I’ve installed and everything is right, checked the plugin in order to be sure that it is compatible with wordpress version (3.9), disabled other plugins to see if there is any conflict, reinstalled wordpress, checked the site without the child theme (the parent theme is twenty-ten), tried to enable allow_url_fopen in php.ini. I’ve checked the plugins in the other sites I maintain, and I had no trouble.
Don’t know what more to do.
And, as if someone were kidding with me, the only youtube plugin that works is the one that was installed in the site, that is amazingly out of date. As a clue, the flikr one stopped working when I updated wordpress.
Any ideas?
Many many thanks.
V.