No video payback - audio fine. Help me troubleshoot please.

Wondering if anyone could help me troubleshoot a weird problem that just happened.  Fired up my computer yesterday, everything normal, tried to play an mpeg file I've played 20 times before, got great audio but no video!?!?  Just a black screen.  Have tried using every media player I have - WMP 10, Nero, Creative, Quicktime - all the same.  It's the same story with other video file formats as well - avi, asf, wmv - all of them.  The strange thing is everything else works fine and I haven't made any changes to the system other than routine maintenance.  Any ideas how to troubleshoot?  Possibly relevant specs (home built) - Win XP Pro (no SP2), Powercolor 9800 XT very moderately oc'd (tried cutting back oc already - no help), latest Catalyst 4.10 drivers, P4 3.0 Prescott oc'd to 3.64 (very stable, have run Prime 95 for 36 hrs with no errors), NEC Multisync FP2141 22" CRT 1600x1200 @85Mhz.  I'm at a loss as to how to attack this because everything else is working fine and it just happened out of the blue.  Went back a couple of System Restore points and that didn't help either.  WTF???  Thanks in advance.

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Lee W, MVPTechnology and Business Process AdvisorCommented:
Make sure your Video Card drivers define your monitor as the primary display.  Video is usally only shown on the primary display (No idea what would have changed this on you if you didn't do it yourself, but that's my guess on your issue)

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RberthugemanAuthor Commented:

Thx for the astoundingly quick response.  Both the Catalyst Control Center and the Windows display properties are recognizing the NEC as the primary display.  I only have one monitor hooked up as well.
Maybe downloading some codecs will help.

By the way, are you able to view other videos?
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I think this is a codec problem.

Search google for "kazaa lite codec pack" Install that and you should have pretty much every codec needed to play files.

What are codecs?
Codecs tell the computer what sort of compression was used to make the video and how it can decode it and play it on screen.
RberthugemanAuthor Commented:
Thanks for the responses !  A couple of follow-up questions.  I initially discovered the problem trying to play mpeg, avi and wma files that I know have worked in the past and that are stored on my hard drives.  I then tested both of my DVD drives with DVD movies and sure enough I get audio but no video with both of them as well.  I'm going to install all new codecs in case the old ones were somehow corrupted but I want to get rid of the old ones first to avoid any conflicts.  But I don't know where they are!  How do you make sure you get rid of all the old ones?  Are they associated with particular software or are they stored in some system folder?  I've never had to deal with this problem before so I'm totally ignorant.  I really appreciate your help.

I've no idea how you would remove the default codecs.

Quite a few come with windows media player, quicktime etc and there already  built in.

If you have knowingly installed some such as divx or xvid go to start, control panel, add remove programs and you should be able to remove it there. But that is only for codecs you have knowingly installed. The ones bundled with media players im not sure how or if you can delete them
I agree that this sounds like a codec problem.  You can identify the codec needed by running GSpot on the file:

If you reinstall the software DVD programs, this will usually reinstall the codecs.
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