New "free" Hotmail accounts are only accessed via webmail.
Many old accounts were "grandfathered" and still work with OE.
If it's an old account try a "server URL" setting of:
http://services.msn.com/svcs/hotmail/httpmail.asp
I've heard about third party software that will let you use OE for new Hotmail accounts. Since I don't use any, someone else should advise you about HotmailPopper (or whatever it's called) & etc.