Problem with my pc (keyboard)?

Hey guys, i took an old pc from my uncle just for some time until i buy my new one. everything works fine except my keyboard which has some kind of problem. I press a on and (while holding to it) it takes 3-4 sec to type a letter. it also produses a sound from the case (like.. tik tik). i changed the keyboard and still the same problem. i tried the usb conection of the keyboard and the circle adaptor too..nothing! its not the keyboards. maybe its sonething inside? got any ideas on how to fix it?