I teach computers at a K-8 school.  This weekend I created a lesson using Microsoft’s Sound Recorder.  Students will record their voice in MPEG Layer-3 format.  I designed my lesson on my home Windows ME machine and then tested everything at school on 3 PCs to make sure that it was all the same on XP machines.  Just before my class arrived I did another test, only to find that MPEG Layer-3 was no longer a recording format option.  Puzzled, I burned up the few minutes that I had before class trying to figure out what happened.  Confused, I bailed on the lesson for today.  After class I checked the student machines (Identical to mine); the four that I looked at could all record in MPEG Layer-3 format.  Somehow, over the weekend, just my PC lost the ability to record in MPEG Layer-3 format.  It lists 11 out of the 12 formats that the other PCs have, but no longer MPEG Layer-3.  It can open a MPEG Layer-3 file, but after clicking: Save as > Change - there is no option to resave as an MPEG Layer-3.  
What in the world could have happened?
How can I fix the sound recorder on my PC?
Thanks, 
eskimo