codec problem preventing mpegs playing

I think this is a codec problem and need someone with more experience than me to confirm it and hopefully advise me how I can rectify it.

It's a bit long but all the information is here and it saves time asking questions about stages already covered.

Windows Media Player will not play mpegs. WMP will play wmvs and avis. I can play mpegs with Nero Show Time, WMP Classic, Power DVD and Quick Time; the same files that WMP won't, so the files are okay. Gspot tells me the codecs needed for these files are installed and okay. WMP error code C00D11CD: Unknown error, which I know is a difficult one to track down. Motion DV Studio and Movie maker will also not recognise these mpegs.

Gspot tells me the following are a problem:
DSH DivXAntiFreeze {79A00187-F159-4B89-981B-F81D51504201} 0x00800001 ** File Missing:
ACM Base MSACM.CEGSM ** Missing file:
mobilev.acm ACM Base msacm.l3codecp ** Missing file:
DSH PCM Morgan Stream Switcher {D3CD7858-971A-4838-ACEC-40CA5D529DC8} 0x00800003
** File Missing:
DSH Stream Subtitle Parser {52780691-D7F8-4335-B38E-EC40280EDC57} 0x00600000 ** File Missing:
DSH Text Subtitle Dest {E2BD78F2-79A2-413D-A052-EE2E91B9D821} 0x00200000 ** File
Missing:
DSH YUY2 Subtitle Mixer {00A95963-3BE5-48C0-AD9F-3356D67EA09D} 0x0080000a ** File
Missing:
DSH YUY2 Bicubic Video Resizer {AA59CBFA-F731-49E9-BE78-08665F339EFC} 0x00800002 ** File
Missing:
DSH YV12 Nero Digital AVC Video Enc {426F6A6F-FEF8-4A5B-8DDC-099E7499EF50} 0x00200000 ** File Missing:

Other strange and possibly connected events:

I tried to play a DVD with Cyberlink Home Cinema after this happened
and had to reset the Region Code.

When I opened an mpeg file with Cyberlink Power DVD an icon for default playlist appeared on the desktop and this happened every time. (May be unconnected though).

Action so far:
I've tried system restore.
I've updated Directx and WMP; rolled WMP back to v.9 and updated again to v.10, without any change.
I ran sfc/scannow
I've uninstalled Itunes.
I reinstalled DivX.
Installed the Microsoft MPEG2 decoder utility
Uninstalled and reinstalled Power DVD and run some codec checkers.
Ran a repair install
Updated Windows, including all software and hardware updates.

It has not made any difference.

This problem arose immediately following my teenage son downloading and running some dubious movies, (we have talked about this on a number of occassions but that's for another forum). I never got to see the movies but I know what they were from the titles as they were still listed in recent documents. I tried to open them from there to see what he had been up to; they never opened and from that moment on I have had the problem as described in detail above. Suspecting a virus or similar, I ran an ewido scan and AVG scan. AVG showed nothing but I've found out that the ewido scan showed a trojan, (my son closed ewido before I got to see the results and which trojan).I've since run AVG, Ewido and AdAware with clean results.

I have had my HJT log checked and it's okay and after many checks and scans I’m confident my system is now clean. This may be a coincidence and a red herring or it may lie at the root of the problem.

As I said I've also run a repair install. The only thing I can think of that is left to try is corrupt/missing codecs or a conflict with another program or something from another program that Windows relies on for playing mpegs is missing. Does the gspot log suggest any action needed?

I thought about installing a codec pack but I read some had caused problems. So I wonder if before I do it if anyone would be kind enough to help me understand this a little better.

I thought that if I could play an mpeg file on another player then the codec needed must be on my PC and therefore the problem must be the player or Windows. Or is it that some players are independent of Windows, so they will use their own codecs, decoders, for example I can use Power DVD, Nero Show, Mplayer Classic? It is the windows specific programs like WMP and Movie Maker that won’t recognise these files.

Gspot tells me the codec needed for the mpeg1 files is installed so I don’t understand why it won’t work. And then I would have thought a repair install of WXP and upgrading WMP would have installed whatever I needed to play mpeg1 files.

Another thing which I thought might be related is that despite having WMP set as the default player for mpegs, when I save an MPEG it is saved as a Power DVD file (icon), WMVs save as a WMP file. It’s as if Windows does, not recognise mMPEGs.

Can someone please offer some help/guidance/suggestions?

Thanks in advance of some kind soul taking pity.

By the way, searching the net reveals this to be quite a common problem but I can’t find anyone posting the solution.

A litle more information to add.

When trying to open MPEG1 files in Moviemaker, Moviemaker reports: ‘MPEG could not be imported. The selected file is not valid or is corrupted’. The same files will open in Power DVD, Nero Show, WMP Classic so they are not corrupted and are supported. Opening them with Gspot tells me they are mepg1 and that the codecs needed are installed.

AVIcodec says everything is okay and all installed codecs are enabled.

Running a codec check with Sherlock I get: ‘Warning the following codecs were found broken.
Audio codec: Morgan Stream Switcher
Video codec: Bicubic Video Resizer, Subtitle Mixer.

Would this be the problem as I can play the mpegs okay with the other programs?

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