I think you should check your hardware, are you using a combined router and modem solution, fiber optic or adsl ?
Restet the router, the Isp may of done a firmware update of the router ect and the internal settings have defaulted to factory settings causing the problem.
sorry i didn't give much information . anyway i fixed it (sort of) , i just went back to windows 7 .windows 8 is full of problems. it definitely wasn't my router because all the other computers in my house worked.i tried almost everything you could think of like resetting my router , computer ,drivers and proxy settings . i even tried a manual ip which worked until i restarted my PC ,when i used it again nothing worked .