If you are using a router and your computer is within an ethernet cable away from the modem, I suggest plugging your computer straight into the modem and see if that works. If that is the case, that means your router is having issues.
Check you hosts file and make sure it wasn't hijacked. I had problems with a hosts file redirecting websites.
There is one site called opendns.com, where you will find Dns server IP addresses, now change to these IPs. This may solve your problem.