thanks for the tip sjurick. it worked partly.
kinda weird. one of the buttons is the "open" button. so i created the text "open" with the create text option and extruded the faces. i deleted the history on all objects (button and text) and was able to do a boolean operation with the "o" and the "e". with the other two letters, everything disappears. also, combining the letters helped nothing. i tried quads and tris on this... anyone knows what's causing these problems?
ps whenever i try to do a boolean operation, objects tend to disappear in general, not only text. so i usually model holes and stuff in objects by hand. only with text... it would be too much work... so i want booleans!