[Closed] backspace not working on chromebook

having a weird problem with my chromebook, the backspace key has stopped working. I have tried reprogramming that function to another button and it still doesn't work, but im not sure that function is working as doesn't work if a programme it to do something else either.

even more strange is the fact it works most of the time when logged in on my mrs profile but not mine or as a guest, using the on screen keyboard the function also works?

anybody have any suggestions? it is an acer C720 if that makes any difference.