okay
first of all changing your MAC address on your router, doesn't always ganrantee your ISpo will let your reconnect to the cable system with that new mac address. most will, but a lot are "registering the mac address to the account and when you changeit , it no longer matches the ISp address. and they do not let you do that..
all that said,
can you access your router ? if so;
Go to your router Configuration for WAN, set your DNS manually for Wan, to 8.8.8.8 and 8.8.4.4 and set the MAC to be the Default. save and reboot router
the IP for DNS I gave you is a public DNS address from google. I have seen ISP DNS get squirrely and want to make sure this is not your issue.
close your internet windows/chrome/google web browsers, and open web browser again, can you access the internet ? no?
right click on network icon bottom right of your screen, select network and sharing, then change adapter setting, right click on your network adaptor, does it have a DNS address marked at that location ? or not ? if yes, change setting to get automatically, save , and reboot PC
try reconnect to internet.