What happened to my steam? [Solved]

Your first step should be to restart client and, if that doesn't correct it, restart PC.
Following that, make sure your graphic drivers are up to date.

You can try opening the settings page in the Steam client, go down to "Web Browser", and click "delete web browser cache".

This should force your client to redownload any images from Steam instead of using a cached version that is saved on your computer. I don't know if it will work, but I don't think it can hurt anything to try.

Edit: I don't know what cased those corrupted files to begin with, but if deleting and redownloading them works, it may be more of a temporary workaround that a fix if you have another problem.