Perhaps you have a Master lock and have forgotten the combination. You don't need to break out the hack saw yet: you can find the combination to a lock. The following steps will work for a Master lock. It will take a little time, but you will be pleased when that lock pops open.
Turn the dial of the combination look clockwise until you reach zero. If you would like, you can do this three times just to be safe. Pull down on the lock as you do this to put pressure on the shackle, or pull up on the shackle with your hand. If the dial sticks, turn it to two then try again.
Note the point where the dial sticks and will not turn any more. Write this number down on a piece of paper. Add a half to the number. If it stops at 5, make it 5.5. If it is 6, make it 6.5, and so on. This is the first number of the combination.
Try turning the dial to the left this time, and make a note of where it sticks. Write that number down and add a half to the number (see step 2). The first number of the combination will be between the numbers you recorded in step 2 and step 3. This is the second number of the combination.
Let the shackle go, and turn the dial to the left just after the second number of the combination (see step 3).
Pull on the lock again, and turn the dial clockwise until you find another point where the dial sticks. Write the number down. Do this twelve more times, writing down the number each time.
Examine your list. If there are any numbers on your list that are whole numbers, cross them off. Look at the list again, and if one stands out, circle it. For example, if the numbers are 8, 28, and 37, then 37 is the number you should circle as it doesn't have an 8 in it. The 37 is the third number of the combination.
Divide the number you have circled by 4. You will have a remainder of 1. If the remainder was not 1, you would take away 2. Since the remainder is 1, add 2.
Write down 3, then add 4 to it and every number on the dial (3, 7, 11, 14, etc). Look at the third number (see step 6). If you have a 35 and a 39 on your list, cross them off.
Try each of the combinations you have written down until you have found the right one. The most possibilities will be 80. You may well find the combination in less.