When TinyMCE doesn't work (or doesn't work right) after an upgrade, in nearly all cases the problem is caused by caching. Could be the browser's cache or a network cache between the computer (where TinyMCE runs) and the server (where TinyMCE is hosted). Normally js and css files are kept in caches longer and are checked less frequently as they rarely change.
Sometimes loading the file directly in the browser and force-refreshing it a few times (while holding down Ctrl/Shift) may force a network cache to check for newer file and update itself.
In any case, after waiting for several hours, could be even couple of days, the network caches will update and TinyMCE will start working again.
bellasvenezolanas, since network cache is stored by domain, not by server, there probably was some stale cache for one of your sites and you had to wait fir it to refresh.
Andrew_t29, no, the file in step 4 shouldn't be blank. This file holds all js for TinyMCE plus all of its plugins. It should either be a text file or a garbled characters (bad compression).
Can you try the WordPress 2.6 demo site http://wp.chrisjohnston.org/ and see if it works right. If yes, download the testing_tinymce plugin from the other post and see if that changes anything when accessing the file directly.