Incredibly Irritating Problem...

[MrMalto]

I have been playing games over my network steady for a while now, out of nowhere, I lose all ability to connect to anyone's server, or host one that others can see. While I can see the server in some games, but not join, other games show no sign of me even being connected to the network at all. I can connect to the internet, showing signs of life in my TCP protocols, and I can also see everyone in my network neighborhood. The ironic thing is, that the ONE thing that I wish to do most, play any game over my network, is the one thing that is impossible at this point, PLEASE someone tell me anything that might allow me to solve this problem!