What should I do if I cannot enter certain characters with my keyboard?

• Check if the Num lock indicator light is on or off.
  When the indicator light is on, you can enter the numbers printed on the keys.
  When the indicator light is off, you can enter the letters and symbols printed on the keys.
  Press the Num Lk key, or Fn+Num Lk keys, to turn the Num Lock indicator light on or off. [Details]

• Check if the Caps Lock indicator light is on or off.
  When the indicator light is on, characters typed will appear in uppercase (or lowercase if you also hold down the Shift key).
  When the indicator light is off, characters typed will appear in lowercase (or uppercase if you also hold down the Shift key).
  Press the Shift+Caps Lock keys to turn the Caps Lock indicator light on or off. [Details]