Unexplained pause after key press

Recently, I notice a strange problem.
The mouse pointer freeze for a few seconds after I press a key on the keyboard. When I press a key down without releasing it, the mouse cannot function at all. e.g I cannot perform Alt-click or Ctrl-click.

I installed a new printer(USB) few days ago but I don’t know if the problem exist before or after.

Spec: XP with SP2, 1GRAM, Wireless keyboard and mouse.