Problem Description:
When try to drag and drop a tool box to the menu bar, it disappears completely from the screen and unable to use it again. Please refer the attached snapshot below.
Steps to Accomplish:
This issue is caused by Windows Update Number KB2973201, remove window update number "KB2973201".
Please use the below link to see how to remove windows update number.
http://communities.bentley.com/products/road___site_design/w/road_and_site_design__wiki/15963.how-to-remove-windows-update-number-kb2973201.aspx
Please let me know if you have any questions on the same.