VALID Argument

Either Lee Chong Wei or Lin Dan will win the ALL England Finals.
Lin Dan lost.
Therefore Lee Chong Wei won.

* The word "Either" has already indicated that only one can win. So if Lin Dan lost, it meant Chong Wei won.

INVALID Argument
All Birds Sing.
Tweetie Sings.
Therefore Tweetie is a Bird.

* Even though the premises are true, but bear in mind that humans sing too. Hence it is not impossible that for the conclusion to be false.