Yahoo mail button not working

Yahoo mail Reply, Forward and Move buttons are not working while Delet and Spam buttons are ok, can not attach (attaching progress bars scroll none stop).
Two computers had the same problem in the same time, Win98 2SE and Win2K. All updated, checked virus and spyware. Tried Firefox and Netscape, problem followed.
I suspect the Windows patches but can not isolate the source. Anyone has any ideas.

Thanks in advance.