Since you didn't mention what version of Windows or what application(s), and given that I don't have a crystal ball, I'm afraid it'll be between difficult & impossible to guess. I will say it sounds like an unusual problem.
Whenever I try to access a drop-down menu containing numbers or dates, I am getting garbage obscuring the data. This occurs on anything that runs on the computer, programs or the browser, but only when numeric data is to be displayed. I have a screen print but I cannot paste it here.
Do you have any idea as to what is happening and how to fix it?