I have added Tiny MCE to my plugins folder but it doesn't appear on the ADMIN plugins page for me to activate.

Any ideas ?

Swap themes, disable all other plugins

Tried that several times - its virtually a clean install of Atahualpa so hardly any plugins anyway.

Have downloaded Tiny MCE 4.0.28 three times now and uploaded but still not showing within ACP.

I did try to install directly via the plugin uploader for zip files and it said something like "no valid plugin found" ..... which seems strange !

where did you get it from? WordPress? what is the actual link?
the only Tiny MCE 4.0.28 (from nuget.org) I see is not a wordpress plugin...

The TinyMCE 4.0.28 I found on tinymce.com is also not a WordPress plugin.