When you plug in a USB device it should give you some kind of notification on this screen (see attached screenshots).
Are you getting anything in the log at all? You may want to start with reinstalling Poseidon from Jen's site, now that you've got all the BB's and other stuff installed.
Note that I've found some devices that just don't work at all - one particular model of USB mouse from Microsoft that's common around my office, amusingly enough. But Dell, HP, other brands of mice and keyboards should all work fine, and flash drives / external storage devices, once you get FAT95 installed & configured.

Did you connect the auxiliary power cable?