Yea same problem here, its been working fine for over 3 months, no problems switching between the 360 and PC, till last night and i have changed nothing.
So I tried a system restore to a week before and still the same problem. Then i tried a full uninstall / reinstall of the drivers and still I can't use the headset or the controller on the PC. It's just driving me mad.
And from what I have been reading all over the net it's a real big problem for lots of people.
Come on Microsoft get it sorted I want to spend my time gaming not pulling my hair out.