"Del" key not working

Hello,

Please help... I have managed to lock my Del key so it does not work. I do not recall what keys I pressed - I think it was the spacebar plus some other key for several seconds and I heard a beep.
Now when I try to use the backspace key or delete something from my Word document it does not work. This is the message which appears:
"This modification is not allowed because the selection is locked".

Many thanks in advance fro your assistance.