Save As dialog is dammaged

On a PC with Windows 2000 Server, all users (except administrators) can read the buttons on Save As… window dialog, and on other windows too. When the window show itself in desktop, the buttons are empty. The same happens with “Search” on top in this page with MS Explorer 6.0. The space for enter search text is missing.
Administrators dialogs are OK.
Any idea? Some *.DLL are wrong? Or is a Security setting wrong with this *.DLL?

Thanks a lot