Windows Media Player 12 No Audio with MPEG1

Suddenly I had no audio when running videos in media player 12 but media player classic played them normally. These were all working normally in media player 12 before.

Eventually I found the problem only exists for audio encoding of MPEG Version 1 Audio.
(All my BLEACH episodes !!!!!! )

Most of my older AVI files have MPEG Version 1 Audio !!
Media Player still has sound for my video files with other types of audio encoding
(For those who dont know how to tell - You can tell what type of audio encoding has been used in a video file by running the appropriate tool e.g. Media Info for Klite codec pack or choosing Analyse Media File for Shark 2007 codec advanced settings)

I have tried
- uninstalling / re-installing sound drivers
- uninstalling reinstalling shark 2007 codecs
- installing most recent Klite codecs
- attempting to repair broken codecs
- Configuring/Tweaking codec settings
- uninstalling reinstalling media player
- Restoring Media Library
- Playing with every setting for my sound card
- Playing with every setting in Media Player including advanced - codecs

Nothing so far has fixed the problem. Every other type of video works e.g. AC3 encoded.
Also theres no problem at all from any other type of player e.g. media player classic is fine

I dont think its a sound card or codec problem. It doesnt look like a windows update has been installed for more than a week so its not that.
I'm running Windows 7 MSDN version with Media Feature Pack
Any ideas???

Thanks Cap
I ran through each step but unfortunately still in the same place.

OK, dont laugh but here's what I did to fix the problem

I exported a list of all the codec files on the PC
uninstalled Pinnacle software (because it also installs codec files)
uninstalled Shark Win7Codecs
uninstalled all media centre/media player/DVD feature options
rebooted
Checked against the codec file list exported earlier to see what files were still there, it was mainly the ones in system32

created a super user local adminsitrator account
(used the local policy editor to add my new account to every privilage that
exists)
used my super user account to take ownership of C:\Windows\System32
modified the permissions on the system32 folder to give super user full control

Used my Super User account to delete all the codec files from system32 folder
Re-installed Shark Codecs
Re-installed media centre/media player/DVD

Now the sound works normally in Media Player for all files !!!
But my webcam in skype is broken

Because my WebCam wasnt working I had to investigate further ....

It seems that some of the files that I had deleted from system32 were not replaced.
The one that was making the sound stop working in media player was Quartz.DLL
(I did get a backup before I deleted them all...)
When I put Quartz.DLL back, the sound doesnt work again.
It looks like media player is using that (broken) DLL but when its not there it falls back to the codec pack configuration which then works ok

I have since read new things on the web for Media Player and Quartz.dll !!!

I still havent fixed my webcam but working on it

with quartz.dll placed in the system32 folder where it belongs,
open a Command Prompt (found in.. All Programs | Accessories) using 'Run as administrator'
type the following command into the black window and press enter:
regsvr32 quartz.dll

I found a much older version of quartz.dll here
quartz.dll free download - DLL-files.com

I used this one, unregistered and re-registered
This fixed my media player issues
I copied back all my other DLL's and now my webcam works

WICKID DUDE !!!!

Yes I had already tried unregistering and regsitering when I found the bogus DLL
It didnt work, but using the older version seems to have done the trick !