Why are some of my user interface symbols rendered as boxes?

Solution 1:

The scrollbar arrows are now drawn using specific characters pulled from the Segoe UI Symbol font. [1]

These square boxes being drawn indicate that Windows can't find the font or load it properly, or can't display the character correctly for whatever reason. People usually see this happen if the Segoe UI Symbol font became corrupted or is missing.

The solution, here, is to somehow reinstall the Segoe UI Symbol font. You can do this by finding the .ttf file for the font on an existing Windows installation and then installing it on your computer. There were places where you could download it online, but they weren't sanctioned by Microsoft and were taken down, from what I can tell. You can see if you can find it that way too, however.

Solution 2:

There may be a copy of the Segoe UI Symbol font in the "C:\Windows\winsxs\Backup" folder.

See "Internet explorer 10 on windows 7 x64 using the wrong image for its UI buttons" for additional information.