It's hard to tell when corned beef is fully cooked and ready to eat unless you have a meat thermometer.
When cooking corn beef you should put the corn beef into a pot and add water to cover the corn beef and bring it to a boil.
The corn beef should be boiled for at least 50 minutes or until the internal temperature reaches 145 F and corned beef can sometimes still have a light pinkish color to it when fully cooked especially when pickling salt is used.
The corn beef when fully cooked should be more brown looking than pink though.