[james muckle] “I have installed K-Lite before…”
That’s what I was afraid of 🙁
This codec pack is well known to be hazardous to Vegas users as it can replace your known good codecs with inferior ones – without your knowledge.
If you ever find the need for a code, use either GSpot or MediaInfo to figure out which one you need and then download only that codec from a reputable source.
[james muckle] “but I don’t know how to fix it”
At this point in time, I recommend wiping your hard drive and doing a fresh install of Windows. After that, reinstall only the programs you need.
If you don’t already have it, I recommend buying a copy of something like Acronis and start doing regular backups of your system. That way, if and when something like this happens, you can be back up and running quickly.