When attempting to edit a HTML document, the Microsoft XML editor may be used. However occasionally this may not function correctly and result in high CPU usage by the MSOHTMED.EXE and MSOXMLED.EXE processes. Using Windows TaskManager to kill the processes may not work also.
To correct this change the HTML document editor specified in Internet Options.
Control Panel - Internet Option - Programs tab - HTML editor field
Reverting back to the original setting also work, but I prefer using Vim for Windows to edit my HTML documents anyway :)