Text editing very slow, difficulties to change font

When editing larger text field (2 or more pages) everything slows down (there is a delay for every task - very frustrating). When "all text" is selected (ctrl+a) and click on Font Menu to change the font, it is difficult to select a new font (mouse arrow doesn't light-up the new font selection) or if it does - I select the new font but nothing happens. Anybody can help? I do have serv.pack1 installed