After windows update Audio & Video Crashes

Hello,
I need some help. I use Windows Vista Home Premium on my computer, a HP with 2048MB memory. Recently (yesterday) my computer just stopped playing all video and/or audio files. I have been using this machine for about 2 years and I've never had this problem before. Now, every time I try to open a video or audio file, my Media Player crashes. At first I thought the program might have been corrupted, but the problem seems to be "widespread", in other words, I tried to open audio files using other programs as well such as Cool Edit and the Zune but nothing would play. Also, even when I try to play youtube videos the browser crashes. I've tried using different browsers but none of them seem to work. My antivirus (avast) is up to date and a thorough scan didn't show any infections. I don't know what to do! The problem seems to have started after I installed my latest windows update, but I can't be 100% sure about that. I tried uninstalling the update but either I didn't do it right or that didn't fix the problem. Can someone please help?