I agree, you really should upgrade your OS. I don't believe your connection issues have to do with your OS being old since you didn't have issues before, but i do definately believe you are going to run into problems down the road.
Definately try typing in ipconfig/renew into the command line interface and see if that fixes the issue. Have you taken the pc anywhere right before this issue started? Sometimes i've seen people actually have to change their IP address from static to a specific IP to get it to work in one area, then they forget to change it when they get home. I don't know your network setup, but your TCP/IP settings both should be set to obtain automatically.