I just reinstalled Halo CE after restoring my computer from the factory recovery partition a few months ago. I can no longer play for some reason. When trying to get the server list, it displays "An error has occurred trying to contact the Gamespy master server". In addition, when trying to host a LAN game(or Internet) it displays the starting network server screen, then displays "Network connection lost" and returns me to the main menu. Honestly, this problem isn't limited to Halo. Counter strike, Garry's mod, TF2, etc. all can't connect to(or even find) multiplayer servers. I can't even connect to Symantec's servers to activate my new antivirus. At this point, this post is less about Halo and more about me sucking at computers. Does anyone have any idea what to do?

Connect to the internet, perhaps? If all your issues are network related, start there. If you can connect to the internet fine, then your issue could lie with your ISP sucking. If not, then perhaps your means of accessing the internet (say, a router) are upset.

Maybe your firewall is blocking the programs from internet access. Try looking for firewall settings somewhere in the control panel

I've tried all these things. I actually only installed norton yesterday. Before I had used microsoft security essentials, and have since removed norton and reinstalled microsoft security essentials. I've tried disabling my firewall and antivirus, didn't help. A friend of mine tried to help me yesterday, and discovered I can't use teamviewer or windows remote assistance either. Any other ideas?

Everything you describe indicates that the ports are closed by an internal (On your PC) firewall. either the Microsoft one or your anti-virus/security software. Check to be sure that Norton is actually uninstalled and not running in the process list of the task manager. Something is closing the ports on your computer.