Is this a USB or PS2 keyboard? I have seen some USB keyboards act up after a key was held in too long. Replacing the keyboard with a different model fixed it. Had this happen a while ago with gaming and holding down CTRL key to speak through ventrilo. The keyboard would eventually become unresponsive. And to get it back I had to unplug the USB cable while system was running and plug the USB cable back in as the temp fix. But when replacing the cheap USB keyboard the problem was gone for good.