- Completely exit the Steam Client & fully restart your machine.
- Open Safari and type: steam://flushconfig then press enter.
- Restart your computer one more time.
- Launch Steam and re-test to see if the fix worked.
Please note that you can't do the Steam Flush/reset in a Chrome browser window, it has to be in IE, Safari, or Firefox. Performing this operation will ensure that there are no issues that could be resolved with a new installation of Steam, and is a good place to start any troubleshooting process.
(Steps are directly from: https://support.steampowered.com/kb_article.php?ref=3134-TIAL-4638)