As XP updates to SP3 and more you find some of these fall away but not all. Try other flash drives.
I have a new HP Flsh Drive v255w which is recognised by my Dell on all USB ports. But it will not operate on any of them, and it's properties show capacity of 0 and usage 0. An older flash drive works fine, as do all otherdevices on thes USB ports. The Flash drive works well on other computers.