I've had this happen on my G5 Mac Pro dual 2.0 GHz. I could not get the front firewire or USB ports to operate. I added a 5 port USB PCI card to give me more ports. A couple of months later, and after some system updates, I forgot that the ports were not working and plugged a flash drive in. The port worked fine. I then tested the firewire port and it was working. I'm running 10.5.8 and I can't tell you why they didn't work for a while. So do the software updates as I don't think it's a hardware problem. The keyboard USB probably doesn't get enough power for the flash drive. Also try the flash drive in one of the back USB ports to see if it is working at all.