Dell 390 sff usb

I have this Dell Optiplex 390 SFF. The USB ports are faulty. I've tried all of them and none of them worked. I can't access the BIOS with my keyboard.  My keyboard lights only light up for half a second if my keyboard is plugged in after it posts. And it does not work at all during that time period.  I've already cleared the CMOS battery twice and it did not help. What can I do to fix this?