Normally I can hit the 'I' or 'O' key to set In and Out points in the timmer window. Now when I hit I or O, nothing happens. I can still drag the in and out points, but miss the 'I' 'O' keys.
Works fine on my setup. You might check the keyboard mappings and see if you inadvertently set these to something else. (how, I can't imagine). Make sure you are looking in the "Trimmer" context.
Otherwise, try holding control-shift when you start Vegas to restore defaults.