Hi, Jay and welcome!
I'm sorry you're having trouble with your safe.
The first thing I would suggest is to chance your batteries. Even though the 'low battery' light is not on, doesn't mean the batteries may have enough power to light up the display, but not enough to actually open the door. You didn't mention your model number, but typically, Sentry safes take AA batteries and they must be alkaline and never rechargeable. You can use lithium for electronics, if you like, as they last longer.
If you don't know the location of your battery holder, please let me know if your keypad is rectangular or round and I will help you with instructions.
Also, make sure your handle is in the complete horizontal position before starting the opening process. You have 4 seconds to pull the handle down, after entering your code and don't allow more than 5 seconds between number entries, as you're inputting your combination.
Please let me know if changing the batteries helps get the safe open, or if you need further help and I will be glad to continue. Thanks!