Guest account password request

I have one pc connected to a router by cable and am trying to get my other
desktop and three laptops to connect wirelessly. The internet is no problem
but i just
get a box asking for a guest password on some of the other machines. This
has started all of a sudden as they were all working until the other computer
had to be
restored to factory settings - now they are not talking.

Any help much appreciated - children cant print homewrok etc....