This is probably caused by the text box editor used in Blackboard since some computer configurations do not display the text box editor screen.
You should try to turn off that editor in order to revert back to the older text editor.
To disable your the text box editor, click on the My SCC tab and then the Personal Information link under Tools on the left side of the screen. On the Personal Information screen, click on Change Personal Settings and then disable the text box editor. You will then be able to use the older editor which should work without any problem.