Unfortunately, the problem seems to be the order in which you installed and uninstalled things.
Yes, I'm sure you can go through codec fixers, 3rd party utilities etc... but I would STRONGLY suggest from experience that you do the following:
1. First, if possible, just restore the computer to a restore point - only if you have one from a date before you installed your programs. If you can't restore, continue to the next steps.
2. You should uninstall your AVID products, itunes, quicktime and any 3rd party codecs.
3. Use Revo uninstaller to make sure junk from these installations are completely removed.
4. Restart the computer.
5. Update Windows. SP2, .Net Framework.... etc...
6. Install the latest version of Quicktime.
7. Install the latest version of Itunes.
8. Restart computer (just for good luck
)
9. Install your Avid products.
10. Restart computer (Just to be sure all drivers are loaded.)
11. Tell us if the problem is resolved. (Most important step
)
It might seem like a pain to do all this but believe me that it will be faster than trying to fix a faulty system.