keyboard goes crazy

Lately, I have had this problem that when I have been away from the Mac for some time, let´s say overnight, it is impossible to log on again.

It seems the keyboard has sent thousands of keystrokes to the Mac, and every time I press on key, hundres of keys is entered in the signing field.

If I try to use the mouse and delete what is entered, it just fills up again. I am not able to do anything: I cannot shut down, I cannot change user and try to log on to a different user, I cannot stop it or anything else...

Very frustrating!

If I shut down using the button in the back, the Mac restarts and everything is fine until next time. I have changed batteries on my keyboard several times, just to be sur this is not at low on power issue.

I have also attached a wired keyboard, just to be able to write my password and to restart theMac, but it does not het. It seems there is some kind of "keystroke buffer or cache" that has run full. But how?

The question is: is this a keyboard problem or av Mac OS-problem? It it is a keyboard problem, I will run off and buy a new one. But I long as I am not sure, I will not waste my money.

It belongs to the story that also my magic mouse behaves strangely, this just startet about a week ago. It keeps loosing contact with my Mac all the time. On-off-on-of, and sometimes it is away for a long time.

This is making me crazy!