My 'ctrl' key has decided not to work. In fact it did this some time ago and I think it was physical rather than a software problem, but I can't fix it by cleaning etc this time. Both the 'ctrl' keys have stopped working. Is there any way of turning them off accidentally in Windows XP? I am using an HP Pavilion N5271 laptop, if that makes any difference.

It sounds as if your keyboard is worn out :-( But there might be a workaround :-) Visit http://www.annoyances.org/exec/show/article02-022 The site tells you how to change your keyboard mapping. "for example...swap your Caps-lock and Ctrl keys" I haven't tried this, but it's worth a shot.

One more thing: Try hooking up an external keyboard to your laptop. This would let you rule out software or Windows XP problems.