I had tried sfc before and it didn;t work.
However....I fixed the same problem on another PC that started after I installed
SP2, Windows Defender, and Ad-Aware.
With WD: No problem! Happy!
With WD and AA: Disappearing downloads! Bummer!
After removing Windows Defender (but keeping AA): Downloads stay! Happy again!
I'm going to try this on the original PC and see if it fixes the problem. Maybe Norton
unfairly got the blame this time...