Sounds like you are inadvertantly placing a button/DRO or whatever off the screen. Best way to avoid that is as Ray has said is to make sure you have chosen a resolution that is suitable for the screen. Another very important thing to remember to do is press the NONE icon after you have placed the DRO or whatever on the screen, if you don't it is very easy to place another where you do not see it and it will then cause you problems similar to what you have experienced.
MachScreen that Ray mentions gets good reviews so might be the way to go but I like screen4 and never have problems with it, maybe I have just been lucky
Hood