我想問點解我在正常情況下入唔到e-mail?

There may be two more reasons:-
1. The Yahoo or Hotmail is busy especially when the date time in USA.
2. Maybe, you had logged in the yahoo or hotmail in other(previous) computer (and do not log out when you leave), In some case, especially in Window Live hotmail, they consider you are logging in in two computers at the same time, so you will have problem to log in again.