OK, usually those steps will reveal the problem.
Could you confirm that you carried out all the steps I recommended, and especially that you complete method 4 without generating any error messages.
We need to get a second opinion on your malware scan, could you do the Kaspersky scan.
The reason is that malware can unregister cryptographic dlls and if it does this after you registered them, method 4 is ineffective.
I would also like you to check that your smart card service is not disabled.
Usually the problem is associated with missing dlls, but it is as well to check.
The following link includes a way of checking your smart card service:
http://joeyahn.tistory.com/entry/Solution-to-Itunes-76-intallation-running-error -when-itunes76-doesnt-start-after-installation
If none of that helps, we need to go back to basic troubleshooting.
First could you check to see if Quicktime works OK, if not describe what happens with any error messages in full.
Next work through the following troubleshooting method:
http://support.apple.com/kb/TS1421
The first stage is to establish if the problem is confined to one account or system wide. Then depending on the result there are a number of things to try - you will already have do some of them.
If you have success could you post back as it will be helpful to know what the probelm was for the future.
If none of that works there is still something else to try.