Your yahoo messenger prob sounds like a script issue,(as posted all over this board) go here
http://www.microsoft.com/downloads/s...displaylang=en and type in script 5.6 ...and follow the download instructions,when it installs reboot.
Im not 100% up to date with symantec AV ,,but are there options in the Anti virus for blocking URL's,active x or cookies?,if so the program may have added hotmail url to a block list,either that or your internet explorer got hit with spyware,malware,or some sort of browser hijack.Reinstall or repair Internet explorer(thats is you want to go back to IE).Depending on your Operating system there are many sites which explain how to repair IE..
Incidently when you were using IE to try access hotmail,did you got into internet options and try lower the security settings?