In windows xp expolorer, it used to be the case that under 'file and folder tasks' there would be a nice little 'restore previous version' option. This gave a list of previous versions of each file. You could then select any of these, and restore them after accidentally saving over one of them or whatever. I do this a lot.

This option now seems to have disappeared. How can I get it back? Microsoft help is, as ever, being entirely unhelpful. Thanks.