Maybe a key on your keyboard got stuck, resulting in your keyboard typing numbers only. Inspect your keyboard closely, and unstick a key, should you identify a stuck one.
Your keyboard's batteries might be almost empty, which is why it started misbehaving. Recharge the batteries for a couple of hours, place them back in the keyboard and it should start working as expected.
If the USB port where the transceiver is plugged in is broken, the computer wouldn't be able to recognize the input from the keyboard. Try connecting the transceiver in another USB port and check if the keyboard would start working as expected.
Removing and reinserting the keyboard's battery is like restarting the keyboard, and restarting it may help with fixing the issue with it typing numbers instead of letters.
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