Weird internet connection issue

Hello everyone, I recently joined the forums in hoping to get some assistance in my current issue. Right now, I use a computer upstairs that is connected through a usb cord (I don't know what they are called) and in my basement is 2 computers, 1 recently new. The computer downstairs we've had for a while has the modem and netgear router hooked up to it. The problem I have is that whenever I go to unplug the usb from my upstairs computer to the 2nd computer downstairs, the new one, that I sometimes lose my internet connection. It will read the network and have a strong signal strength but it won't connect to the interent. The first 2 days it was connecting, the reason I do this is to play some of the computer games on this computer as they are better suited for it. Anyways, after that I spend about a half an hour or longer trying to get my connection back on the main computer with the router and modem working properly with the old computer it was oringinally connected to. The problem is that I always try to reset it by taking the cables out and plugging them back in and at times it will read for example sent:140, received:11 or sent:5500, received:5100 and will still not work at times. I was wondering why I lose my connection to the downstairs computer when I unplug the upstairs usb, shoudlnt that only lose connection to the upstairs one. When I plug the usb into the new computer to play games I have to get the connection working on the old one again working before it properly connects to the new one. These 2 computers are sitting right next to each other but I have gotten the new computer to work before several times this week playing on it for hours at a time with the usb connected in it and the modem and router in the old one. My questions are why do I lose my connection when I unplug the upstairs usb, how come it shows a strong signal and sent and receive bytes but wont connect to the internet (xp on the old one and upstairs, vista on the new one), and why does it work time to time. I know this was a length post but any input would be appreciated.