-if you have the type with the vertical bar lock as opposed to the round pins, many times something inside will jam the runner and prevent the slide bar from moving--maybe try to wiggle it a bit in the opposite direction from where the door opens.
And make sure your sequence is correct if it has a dial lock:
Start with dial at zero-Turn left 3 times stopping on first number of your combination, example if the number is ***** count the first time you pass 25,and then two more rotations stopping at 25. Then turn dial to the right stopping at the second number --when you are at the second number, turn dial back to the left until its stops at the third number. As the third digit is getting close, you will feel tension in the dial as the third tumbler lines up.--
If that fails, here is a link to Treadlock (now owed by Granite Security in Irving, Texas):
You can call @(###) ###-####if you are around Austin, TX . They will help you to crack this safe.