Do you have the full-paid version of PrPro, or the trial?
If you have the full-paid version, have you updated to CS4.2?
If you have the full-paid version, and have upgraded, it is possible that your installation has reverted to the "trial." This has happened to several recently.
You will want to Deactivate your copy of PrPro, if that option is available (not grayed out), then uninstall CS4. Run Adobe Clean Script CS4 several times, rebooting between each run. Then, install CS4, and do all of the updates, before you use the program.
That should get your MPEG back.
PS - Welcome to the forum!
Heh, currently I got the K-lite installed.
Should I uninstall it, then? I tried reinstalling and updating to no avail.
Well, K-Lite usually installs FFDShow, which messes up many Adobe programs. It also overwrites many good CODEC's with hacked versions. I would first uninstall everything related to K-Lite, including FFDShow, if possible.
Some users have found that only a complete wipe and reformatting of their system HDD will get rid of some of this stuff. I am anything but a fan of any CODEC packs. They are usually a horrible problem.
Good luck with uninstalling. I would also run CCleaner, or similar, when done, and hope that you can clean that stuff out.