KB3121wt Keyboard Doesnt Work

We have a few sets of KB3121wt keyboard with mouse. Two of them does not work now. There is no response when I press any key. The only key that works is the search key, which brings up the Windows search bar. If I turned it off and then on again, the battery light will be on for 3 sec and then goes away. If I turned it on with a key pressed, the battery light will be flashing for like 10+ sec. I tried changing the battery, including swapping battery with other keyboards that still works. Other keyboards still works just fine using battery from this one, but this one will not work regardless if it's a new battery or if it's from other keyboard. I checked the Dell peripheral manager software, and it is actually showing 100% battery. For the first keyboard that does not work, I tried unpair and then repair it, but it simply wont pair. Does anyone know what is going on?