Can you post a screenshot of the gimp interface with tool options and layers showing.
However, at the moment best guess:
Check that dynamics are (1) Dynamics Off also (2) brush / layer opacity and (3) the type of brush has an effect, do not use an animated brush.
Make sure what you need to erase is on the active layer.
However, at the moment best guess:
Check that dynamics are (1) Dynamics Off also (2) brush / layer opacity and (3) the type of brush has an effect, do not use an animated brush.
Make sure what you need to erase is on the active layer.