I have a A500 with the same problem, it could also be your KB MPU (keyboard IC). Most likely one of the Amiga keys doesn't work; try if you can move the mouse by pressing LA + Arrow or RA + Arrow. If the mouse moves the Amiga keys are fine, so you can check CTRL. If all 3 keys function normally it probably is a reset line failure somewhere.
There is a software fix for this though; reset command on aminet.
Although, if the amiga really crashes it is no good
