Remove the keyboard in the device manager to let it redetect the next boot.
Be aware that some keyboard loggers show themselves with such anomalies. Be sure to use all the good tools to be sure the pests are non-existent.
Returning from 3 months working away, my wife said "something strange is happening with the computer . . . . . "
Whenever I open a menu it is as if the down-cursor key is being held down, making it impossible to navigate etc.
I have tried a different keyboard - no difference. I can boot-up into safe mode, navigate to the device manager but no problems are highlighted. I downloaded (via the laptop I am using now) RegCure but haven't got it working on the desktop PC (menu won't stay still!!).
Both laptop and desktop are using XP Pro Sp2.