Vista - Sound and Video problems

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?

You may have Windows corruption either due to undetected Malware or registry cleaner use.
Suggest to Use System restore to restore to point before Windows corruption,
and scan system here with eset's NOD32:
Free ESET Online Antivirus Scanner

See post #2 in this thread for further info:
blue screen