Right click on the drive and then open properties on the bottom of the context menu that pops up and see if the box is checked for them to record. XP sometimes came without codecs, Win 7 as far as I see only let's you pick a priority deck. It won't let both my decks work at the same time. Kind of odd, but you don,t usually need both, but a pain to have to check each time.
While your looking at properties make sure on the General page it says' the decks or drivers are working.
Still know, go to Admin tools and check out the decks on the device manager, it will usually have a little yellow marker if somethings wrong.
PS you can do the same right click trick and properties in device manager