First question is what operating system and service packs are installed.
If you have WIN XP with SP1 or SP2, then I would uninstall the USB devices and controllers and then power down. Wait a few seconds and power the unit on. It should reinstall the newest USB drivers (The USB 2.0 ones). Let us know what happens.
If you don't have WIN XP or SP1, then you need to upgrade. If you O/S is other than WIN XP, you will need to go to Microsoft's site to determine the maintenance level (SP oand/or upgrades) that will enable USB 2.0 and then upgrade, uninstall the old USB devices and the let the system reinstall the new USB 2.0 devices.
All the USB ports on the 870 should be 2.0 - or at least mine are and I have connected external devices to all three.
After you found out that WIN2003ADV could not be used on the 8790, which O/S did you install?