This is a quit common occurance with the installation of a codec pack like K-Lite, especially the Mega Pack. Although it can be a very usefull and worthwhile download for those who have a firm understanding of the functions of codecs, and for awhile it will be an asset for those sho are not as savy, but as I am speaking from personal experience, everything can change in a heartbeat.
The first inclination is to install the whole thing......this is the first mistake. Second, there is the desire to install several different software titles to experiment with. The result of these factors can be the installation of the same codec multiple times, orphaning certain file extensions, and confusing the user to "which app plays what". A "stepping on eachother's toes" result so to speak.
I am assuming that you are using Windows XP SP2, and if not let me know.
Start by creating a System Restore Point
then you can start uninstalling VLC, K-Lite Codec Pack, Media Player Classic, BS Player. If you use the free versions of these titles, I recommend uninstalling them as well......QuickTime, RealPlayer, DivX Player. Also, if you have downloaded any independent codecs other than those for Windows Media Player, Uninstall them as well.
Note that you should always uninstall software using the provided uninstaller, all of the mentioned apps come with one, and just deleting them will leave program handlers and other corrupted files. You will need to empty your Recycle Bin, and do a fresh Boot-Up before starting the reinstallation process.
After you have got rid of all the mess, I recommend downloading and installing the following:
1. Media Player Classic
2. QuickTime Alternative
3. Real Alternative
4. AC3 Filter
Also, for better management of future media playing needs, I suggest creating a folder in C:\Program Files......named Audio & Video or something to that affect. The path will look something like this...C:\Program Files\Audio & Video\media of your choice...
Install any standalone codecs, media players, and so on in this folder, that way you know where everything is at. The above titles should cover you for most popular formats, and if you find one that you need and don't have....search Google for it, and install just what you need, this will ensure that you don't do any over the top installs.Also, QiuckTime and Real Alternatives will prompt you to install Media Player Classic, make sure to untick the option to do so in each of the installs.
I also don't recommend installing VLC player and MPC, to many conflicts, and like I said previously, if it won't play right, look at the file extension, and search for it......it's out there and you don't need to install a big codec pack to enjoy your media entertainment.
If you are not sure about something, don't hesitate to ask, I hope that this helps,