Hi GF.
I HAVE seen the problem and the foregoing WAS the answer. Worth a try.
If you are NOT using USB. Check that the keyboard and mouse connections in their respective ports are actually IN their respective ports. It is so simple it can be missed.
The ports are marked Keyboard and Mouse but they can be the same fit and it is dead easy to put them in the wrong port!
The problem you are encountering could be caused by this.
Worth a try!
IFR