See if accessing the Power Button menu allows the USB ports to work again.
You can try holding the power button as instructed in page #62 http://downloadmirror.intel.com/23089/eng/D54250WYB_D34010WYB_TechProdSpec06.pdf
Thanks for the idea - unfortunately, doing this doesn't make the system enter BIOS.
Looks like I'm running out of options.
EDIT: Actually, rguevara, your suggestion worked when I tried it after a shutdown from within Windows (attempting to enter the Power Button Menu from a cold power-on doesn't work for some reason). Thanks again!