The original manual, in case you still would want to refer to it, is no longer available from Sentry's site, but this manual might be helpful, from Home Depot:
As for the batteries, replacing them would be the first thing to try:
Place both hands upon the keypad, then pull it upward to unlock it from the door, then pull it toward you to access the battery compartment. (This applies to some models with keypads. For other models it might be a somewhat different method. See several below:)
Try twisting the keypad counter-clockwise instead! on some models that is the solution to getting the batteries replaced.
If there is a retaining screw at the bottom of the keypad, remove that first.
In some models, there is a pinhole below the buttons of the keypad, you insert a paper clip into that hole and push down, then while pushing down you can slide the keypad to the right.
Let me know *if* none of these methods work. There may be more suggestions for me to offer.
Then, if the batteries have leaked brownish corrosion onto things, you will need to clean it off the battery compartment terminals until they are shiny and metallic looking at least on their battery-contacting surfaces again. This is best done with cotton waste or cotton swabs, moistened in rubbing alcohol. (If the corrosion is tough, rubbing a bit with sandpaper first might help.)
If replacing the batteries still gets a green-light-but-no-unlatching, you may need to lubricate the safe's workings, with safe lubricant or lock lubricant. This is a type of silicone-powder lubricant that may be purchased at a good hardware store.
Do not use grease, oil, nor WD-40 on a safe - it will ultimately be bad for the workings.
Blow the safe lubricant or lock lubricant into the latch at one side of the door, let it sit for 20 minutes, and try unlocking/unlatching the safe again.
Let me know how it goes, if you would. I may have further help to offer.
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