Yesterday Microsoft did a total of 38 Windows updates on my computer (Windows 7 [Version 6.1.7601]). Since that update Audacity flatlines (as in no input) from any source (in the past I strictly recorded output sent to the speakers). I have no microphone(s) so I have no way of knowing if recording from a microphone would work, not that it would really make any difference given what I use the program for (recording segments of Public Radio shows). I did a forum search for “Windows update” but came up with nothing useful.
Tried uninstalling the the associated audio drivers and reinstalling?
Along GoG’s lines, see http://wiki.audacityteam.org/wiki/Updating_Sound_Device_Drivers#Windows_Update .