Common reasons for Yahoo Mail not working properly include internet connectivity issues, server outages, and browser-related problems. If your internet connection is unstable or slow, it can disrupt Yahoo Mail's functionality. Server outages, which can be caused by maintenance or technical issues, may also lead to temporary disruptions. Browser issues such as outdated caches, cookies, or extensions can affect how Yahoo Mail loads and functions. Additionally, account-specific issues like incorrect login credentials or security concerns may prevent access.