i jst dont understand why my usb gets really hot on my computer
See: "USB devices are powered, meaning there is an electric current running through them from the second they are plugged in to the second they are removed, unlike PS/2 where there's just a signal transmission. Because of this, they tend to get warm, and some do get rather hot."
Maybe the other MoBo runs more current to the USB, I don't know, but warm, even hot, USB devices are normal; different Boards = different manufacturing = different specs. If they ever get too hot to hold though, then you have either a faulty USB device or a faulty USB MoBo port. While it may be nothing, USB issues on a MoBo are a sign that the Board may be failing, though usually the ports will simply stop working.