I agree with dmore and I've seen this at work.
The window's size is set to a specific value, but you have your font set bigger than the programmer planned for. When everything in the box gets scaled for your font, the buttons are getting pushed off the bottom of the page, and out of the window.
If you don't know how to change the font, we'll need to know the operating system you are using to guide you through the steps.
RM