I will say it before Harm M. flames you on this subject.
Get rid of the K-Lite Codec Pack that you installed then I am certain he will tell you... reinstall your O.S in a clean system.
Dont take my word for it but.... be prepared
despite sounding very time consuming, I think thats exactly what I'd doing in this case. something has gone horridly wrong (a file has been overwritten somewhere) and a fresh OS sounds like a pretty good aproach to me!
Lesson 1: Don't convert unless you have to. Every conversion costs quality.
Lesson 2: Don't install codec packs, unless you really enjoy formatting your disk and installing OS & programs.
Lesson 3: If you skipped lesson 2, you will learn a lot about installing Windows and setting up from scratch.
Thanks guys for all your help.
I was just seeing if I could avoid doing it but I will take your advice and
I know this is stating the obvious: Please make sure to back up your project files and media before you format/reinstall.