Below are a series of guesses for a 4-digit combination followed by hints. An "X" indicates that there is a correct digit in the correct place, and an "O" indicates that there is a correct digit out of its correct place. With these hints, try to deduce the correct 4-digit combination. All four digits will be between 1-9 and all will be different.

7 4 9 3 - OO
5 3 1 2 - X
9 8 6 5 - OO
8 1 7 2 - OX
6 3 4 9 - XX

I think this one works, but I am not sure that it is the only possibility:

Sorry Lex, but the first line in the clues eliminates that answer. There would have been 3 X's or O's.

This might do it:

Ding ding ding ding ding!