As Hit_Factor said, there is a Key Lock function that can be enabled by one of the programmable buttons. Pressing the button will toggle it on/off. You'd need to figure out which button it is.
Alternately, I'd be curious to know if "keypad lock" is what you are referring to?
There are ways to program it so some keys do not function. If it's just certain functions that do not work, you'd need to look at the programming.
Also, there is a way to read, write and read/write lock the radio so it cannot be read, written or read & written from the software. That requires either knowing the password to unlock it when you connect to the KPG-111 software (which the seller may not have depending on where/how he got it) or having the "Engineering Software" key.
Knowing which one you are referring to would help us point you in the right direction.