only did a quick look at KB's. appears the one that didn;t install is maybe a microsoft bug that hit many

but that first one

Update for Windows Media Format 11 SDK (KB929399)

Start64!Install this update to address the DRM subscriptions service’s inability to extract metering data from certain portable devices while attempting to synchronize metering data on a client computer running the Microsoft Windows Media Format 11 SDK.

Update for Windows Media Format 11 SDK for Windows XP x64 Edition (KB929399)

u might:
- maybe coincidence, but try googling drm KB929399
- Look into uninstalling those KB's
- Have you just tried uninstalling all of Media Player (try things) and then reinstall

I also just changed my processor from a Sempron 3100+ to an Athlon 64 3300+, then all hell broke loose with my media player. Same error messages & hangs. I uninstalled MP11, rebooted & reinsalled MP11 only to have same problem - Here's something that might help - I run 3 hard drives in my system, all with the same version & upgrades = Windows XP Home SP3. I have restarted my computer, booting up to each different hard drive only to have the same problem occur with MP11.

I know Windows XP does some strange things when we change a piece of hardware, like the motherboard or processor, and I don't think it's a coincidence that this started right after we both installed a new processor. But what do we do about it?

If you replace your CPU to a different chipset (as you have done)
Then you must run a Repair on Windows

For any further help, please create your own unique thread
As your scenario is actually different to that of member red1776