SQL Server Reporting Services Security

Hi

I have an issue where when opening the home page of my SQL Server Report Server via it's name http://HOSTNAME/reports/Pages/Folder.aspx

It automatically assumes I'm the domain administrator and states

If I access the server by changing the host name to the IP Address in the web address it then prompt for credentials which allows me to login as myself who is the content manager so I can now change things. Annoying thing is, it prompts every time I do this and doesn't store my username and password.

If I then change it back to the server name it assumes I'm the administrator again but I cannot get these credentials out of Internet Explorer so I can login as myself.

Never had this issue before, only since I've...