Some electrical outlets not working
My best bet would be you have a loose splice or connection. You need to go through each box and see if there is a conductor or wirenut that is not making a good contact. Many times if someone has used the pushins on the back of receptacles and switches, they become loose and stop making a good connection. That is why most of us were trained not to use them. Take each splice and hold the wirenut with hand and pull each individual wire to see if they are making a good connection. 

You do need to fix this problem since a loose connection is slowly burning and arcing and causing the conductor and is insulation to be damaged. You might try to measure the voltage a each of the receptacles not working and see if you are getting particle voltage like 70V or something. This could give you an idea of how the circuit is run and Where your problem may be.

Good luck