I don't often admit it, but I actually use WordPress for my other blog: http://www.osirisguitar.com
Usually, upgrading to a new WordPress version is smooth sailing but this time the editor broke down completely - TinyMce didn't show up at all, just a white empty space.
Turns out the SoundCloud is Gold plugin is the culprit. Luckily it's only the editor buttons that are broken, the frontend part of the plugin still does its job (which is inlining SoundCloud players in your posts).
To keep the plugin active but deactivate the broken buttons, edit soundcloud-is-gold/tinymce-plugin/soundcloud-is-gold-editor_plugin.js.
Comment out the functions starting at lines 123 and 138 (those that bind to the mousedown event in TinyMCE).
Bonus info: the Triberr plugin for WordPress is a real slouch - it added 1,2 s load time to each page. Don't use it.