First, you need to figure out why once you get a sequence wrong, you can never advanced to the next level even after entering the correct sequence. For example, purposely get a sequence wrong on round 2 or 3 and then try to enter the correct sequence. You will see that no matter how many times you enter the correct sequence after Simon plays it for you, it will not allow you to move to the next level.
On a side note, you really need to make it clear to the user that they have clicked a button by lighting up the button and making a sound. Many times, it is know for sure if I clicked a button or not and since their is no feedback given.