Blank WYSIWIG buttons

Almost all of the buttons in my page/post editor on the back end (the WYSIWIG editor) are blank gray squares – looks like this. They appear to still be functioning but the images aren’t there so I can’t tell what they control for the content styling. I tried reinstalling the newest version of WP to no avail. It started happening with the most recent update. Any help is appreciated. It’s always something…