Keyboard problem - type L get A

Hello,
For the past 2 days when I press the L key I get an A but this is only when I am in a login site asking for login name and password - the keyboard will only type the correct letters if I press the insert key and keep it held down.
If I go into a Word document or any other document then the keyboard works as it should do.
I think maybe I've inadvertantly pressed a key which has somehow messed up my keyboard - can anyone help??

Thanks