Is this a new house or old? Check the outlets, see if the wire pushes in the back or screws on the side. If it pushes in the back it may have worked loose. Also see if the circut is on a GFIC for some reason, are there only two outlets that do not work? If you have replaced something make sure that the wire nuts are tight, that you didn't knock something loose as you shoved wire back into the box.