Win7 is relatively new and I haven't heard much about its use in Vbox.

If I was troubleshooting, I would check to see if the things you mentioned
work properly on the host machine first. For example if a flash drive has
not been mounted or the sound board has been muted in the host it would not
work in the guest either.

Next I would check the settings in Vbox under the VM you are working on to
make sure that you have made the devices available to the VM. Once it is
booted, I would check the status bar at the bottom right to make sure they
are checked and in use in the VM.

If everything checked okay then I would check the guest OS to see if the
drivers are installed properly. With XP, if you don't have the proper driver
the device manager in the control panel will show a question mark beside the
device. I am not sure how the control panel in Win7 works, not having used
it.

If the device is not available it would not show in the list at all and
there would not even be a device name. This would be a clue to go back to
the settings and make it available. If it was available then I would try a
different Vbox drive in the settings of Vbox for that VM. You need to
shutdown the Vm to do this.

It is important when trouble shooting to be systematic and eliminate the
most obvious ones first, only changing one thing. Write down things you've
tried if you can't remember them.

Lastly, I would check out forums where Vbox and Ubuntu are commonly used or
one that is more general such as Linuxquestions.org.