[SOLVED] usb don't work in virtualbox

hi
i m running ubuntu studio 13.04 kernel 3.8.0-34-lowlatency,
using virtualbox 4.2. 10
having installed windows xp 32-bit as my guest os

My problem is that the the guest os cannot recognize any usb device connected to any port of the pc. the ports are usb3, compatible with usb2 and the two front are usb2

in system--> users and groups --> manage groups I' ve added my user name to the vboxusers, vboxsf and lp groups.
I ve also have installed all the virualbox sidepacks from synaptic.
and the extension pack from virtualbox.org
VBoxManage list extpacks
Extension Packs: 1
Pack no. 0: Oracle VM VirtualBox Extension Pack
Version: 4.2.20
Revision: 90983
Edition:
Description: USB 2.0 Host Controller, VirtualBox RDP, PXE ROM with E1000 support.
VRDE Module: VBoxVRDP
Usable: true
Why unusable:

any suggestions?