I have a computer that is currently running Windows XP SP2. This machine is a Dell Dimension 510. It only has USB ports for keyboard and mouse - there are no PS2 ports available as is from the manufacturer. I am able to utilize the USB keyboard during boot sequence. I even tried a wireless USB keyboard, and it works fine during the boot sequence. However, once the Windows XP User Select / Login screen comes up, the USB keyboard and mouse stop working. Ports are still receiving power as confirmed by digital multimeter. I ran a boot CD, booting into Ubuntu, and the USB keyboard and mouse work just fine there --> This confirms that this is NOT a hardware related issue. I have unplugged the machine and let it sit for several minutes, comes back up and does the same thing. I am unable to test PS2 keyboards as this machine does not support PS2. I have tried all USB ports and have tried different keyboard / mice combinations. Once you get to the XP User Select / Login screen, the USB mouse and keyboard stop working. If you need any additional information, please let me know and I will be happy to supply. Any idea what may be the cause of this, and how to resolve?