This worked for me before, so hopefully it will work for you as well.
What I suggest you do is install the launcher directly from download (not from disc, as that will reinstall the whole client as well) so all the directories are set up properly, then when it starts to download the client data files, stop the download and paste everything from the three Elder Scrolls Online folders (depot, vo_en, and the other one whose name escapes me) into the \Zenimax Online\The Elder Scrolls Online\ folder (or \Zenimax Online\The Elder Scrolls Online EU\ if you're on the EU server). Start up the launcher again and it should no longer need to download anything.
I recommend you run Repair afterwards though so it can check that everything's there properly.

Thanks Eno might come in handy for next time or someone else I thought it would be something like that but didnt want to go through the install pain again