After i formatted my Dell Optiplex GX270 and did a freshed installation of Windows XP, my USB doesnt work. I downloaded Service Pack 1 to fix the yellow exclamation mark so it did. But when i connect my devices to the usb port, it doesnt detect it. I know my usb devices are working fine because i use it on my other computers. For instances, my Joystick. It is working because the lights for it turns on, but windows xp does not detect it. What is wrong? Please help me!