Can't access Internet... firewall problem?

Hi,

I have a PC and a laptop networked through a homegroup. Both show Internet access, but I am only able to access the Internet through the laptop. I have done much troubleshooting trying to figure out what is going on with the PC (which is my kids' computer, and they probably downloaded something they shouldn't have).

I've tried Firefox, Chrome, and IE. Right now I'm getting odd, limited access through Chrome... allowing me to do Google searches, for example, but then I click on anything from the search and it doesn't load the page. It will not go to most pages at all... just Google seems to be working. FF is giving me nothing, but seems to allow me to search Norton help pages.

I've done many things to troubleshoot including resetting the router, leaving and rejoining the homegroup, running various diagnostics, I did a system restore, etc.

Is this a firewall problem? When I go to NSS settings, Smartfirewall is checked but grayed out and I cannot change any settings. This is NSS through Comcast/Xfinity.

Thanks for your help.