As a  new learner of Zope & Plone (Plone 2.5). 
I am slowly working through ZopeBook-2.6.
Most going well but  suddenly all screen icons have disappeared!.
All I see is the alternative text. 
* Probably the last thing I was playing with is on page 110 of ZopeBook-2.6.pdf
Where I viewed directly "http://localhost:8080/p_/ZopeButton" - which still works
• And did some experimenting with "standard_html_header"
• It was about this stage that icons began to disappear
• I have done some undos 
• I have restarted zope
• I have restarted computer
• I have tried an zope.org archive search without success
Everything else seems to work OK
Any help appreciated.

George Wright