Using AOL for a long time can create some issues that may bother you. Http error 504 in AOL mail such an issue that can prevent you from further activities. Now to remove this issue look into these steps:
• Try to open the web page by pressing the refresh key
• You can tap on F5 and try to open the webpage
• You need to do this several times
• Then restart your device along with the modem and router as well
When it open you can try to log in to your AOL account. If it is still not working you should call at AOL contact number for further support.