There are a couple of things which can cause that. There's probably a switch in the BIOS which can limit the USB speed. Go to the Advanced Menu in the BIOS and then select USB configuration. Make sure that "USB 2.0 Controller" is enabled and that "USB 2.0 Controller Mode" is set to "HiSpeed". Also make sure you have your chipset drivers installed. You can get the latest chipset drivers from
here. Download and install the "INF Update Utility [INFINST.EXE] (1541KB) 6.3.0.1007 12/16/2004".