Backspace Button Crashing/Black Screen on laptop

I must have inadvertently hit something today, because my Backspace button now "crashes" -produces a black screen - on my laptop. It shuts down the system within about 5 seconds and I have to power back up - but when I do power it back up, it only takes a second or two, my work is still there and my XM radio comes back on.
Has this happened to anyone else and can anyone explain how I might be able to "undo" whatever it is I have done?
Thank you in advance !