Please help me!

For the past month or so, my computer has a one in three chance of saying this message, and the simply not connecting. I looked at all my firewalls on my computer, and I can verify it is from that. Weirder yet is that other peoples computers (my friends laptops) get the exact same glitch, but only when they are at my house.

Why is this happening? How can I fix it?

Thanks, -Darokrithia