Board Thread:Support Requests - Getting Started/@comment-6026139-20140120061615/@comment-1330470-20140122014612

According to User blog:Rappy 4187/Technical Update: January 14, 2014:

The classic/original visual editor is currently disabled in Internet Explorer 11 due to major changes introduced in that version of the browser. The new visual editor is not yet supported in any version of Internet Explorer, though support is planned for the future.

I'm afraid that until these issues are resolved, you'll have to consider a different browser, or learn to adapt to Source Mode.