It sounds like the RB window is larger than your screen. Maybe you switched monitors or changed the resolution recently. I recommend temporarily changing back your screen settings so you can adjust the RB window size:

1. Right-click on desktop and select "Display Settings". Adjust the slider that affects the size of "text, apps, and other items". You might also try changing to a higher resolution.
2. Once you can see the entire RB screen: scale RB down to a smaller size and close it. RB will save its most recently used window size.
3. You can then change your screen settings back to the desired scaling/ resolution. When you re-open RB, it will open at the smaller size, and you should be able to see the entire window.