Found a bug!
The woocommerce start, the WordPress TinyMCE visual editor does not display the edit toolbar in IE7 browser.
If you stop woocommerce plugin, everything back to normal.
Why did not I upgrade IE? In fact, I use IE10, but I have a contribution form on the front end, this form call the WP editor, so when the user wants to submission, if he is IE7, will be facing this bug.
And I have no way to require all users to upgrade your browser. Request fast to solve this bug!