Stop! Before you connect two PC's with a cable... (USB)
If connecting two PCs via USB connections, make sure you are using a "bridged" or "networking" USB cable. It has a small electronic circuit in the middle allowing the two PCs to talk to each other.
If you use a regular "A/A" USB cable (a stardard cable with a USB connector at each end), you can fry the USB ports, their power supplies, or even a motherboard.