Hi, I am Dave, I will help you with this.
1
Open Command Prompt, then run this command and press Enter:
msdt.exe -id KeyboardDiagnostic
Run that Keyboard Troubleshooter to see if that can solve the problem.
2
If that does not resolve this for you
Open Device Manager
Expand the Keyboards section
Right click your keyboard and choose 'Uninstall'
Then restart your PC
3
Id neither of those options resolve the problem, there may be a keyboard shortcut to lock the keyboard on your keyboard, are you using an internal keyboard on a laptop or an external keyboard on a PC?