Modem randomly blocking websites

I just got a new xfinity modem at home and I am trying to access some sites that I was able to access before. However, mymodem is blocking those sites. I am able to access them through work computers and through my cellphones when they are not on my home network. I read some posts online where others seem to have the same problem and they were able to resolve it by power recycling the modem or spoofing MAC address. I did not have success with the power recycling and do not know how to do the MAC spoofing. Does anyone have a solution to this problem?