Actually, there is a way to reprogram (actually add a different code), but you must be sure that the combination you have now is absolutely correct. If that is not the right, original combination, you can't add another combination. I'm assuming you don't have your original owner's manual, but there is a downloadable one online, with these instructions about programming a 'user code' and 'user pin', which are temporary. The user's manual is in a .pdf file and difficult to send, so go to the following site, scroll down to 'owner's manual' or further down, 'view manual' and click on there.
It might just open on your page or go, as a file, to your desktop or elsewhere on your computer. Read the instructions in there, towards the right hand side of the page and try one or both, to see if you can program one of those different codes. If that doesn't work, then you don't have your correct original combination and will need to request it from Sentry, here--just follow all directions:
There are still other things you can try, now: take a rubber mallet or a hammer with a towel wrapped a few times, around the head (so you don't damage the safe) and hit the door above and below the keypad a few times. This may loosen up the opening mechanism if it is stuck, after not being opened in years. Also, hit the safe door, all around and concentrate on the upper left hand corner of the door, as the rubber gaskets in these safes can swell. You can push in on it with your body, as if you're trying to close it. You can also tilt the safe to the back, front and/or sides, to redistribute the contents inside, as something may be pressed up against the opening mechanism.
When entering your code, don't let more than 5 seconds lapse, in between numbers and also, start with the handle completely horizontal and then, you have 4 seconds in which to pull it down after you enter your code. If it won't go down, try pulling it up.
Let me know how you do. Thanks!