Advice..

[trevius]

Just 1 more thought on this that I didn't think of before; If you are running any kind of P2P or Torrent software on any of the PCs in your network, they will almost definitely cause connection issues with almost any internet downloads or programs. They can use hundreds of connections to different end-points and overload your internet connection or router. Make sure you limit the bandwidth allowed for such programs as well as limit the max number of connections that they can use. If you don't use any of these types of programs you can ignore this post, but if so I would try turning them off and see if that helps.