OK, so there have probably been two problems here. The first was that you were using an older version of WordPress than we support. The second seems to relate to Live Countdown Timer by Turcu Ciprian – with this activated for some reason the wp Javascript object is no longer present.
Nor does this only affect our plugin. With Live Countdown Timer still active try creating a new post and using the Add Media button (above the editor) – you ought to find nothing happens there either.
Deactivate it however (and flush your browser’s cache) and you should find it all works as expected.