What type of adaptor are you using on the PC Tower? Does it have a removable antenna, or can it be moved itself. If so try moving it around a little and changing the antenna from vertical to 45 degs then horizontal. I don't think your USB and hub are the problem.
After that try changing the the Channel for the WiFi. Do you pick up any other WiFi Networks close by? If you do they may be interfering with each other. Try to keep the channels 5 apart (ie 1 or 6 or 11 and so on).