Welcome to the forum.
My first guess would be that after the restore, you have not installed any program, that adds the H.264 CODEC to the system. This can be done with Apple's QT Player (latest versions), and that is good of other aspects of editing with PrE.
Now, Apple's is not the only H.264, and some mfgrs. tweak H.264, so I would also look on the utility disc., that likely came with your camera, as Go-Pro might have a tweaked version of H.264. That version might be a separate install, installed with the camera's driver, or perhaps as part of an editing, or cataloging utility on the disc.
Too bad you did not post here, first... many people have reported problems with codec packs... sometimes to the point they had to wipe their hard drives (after UN-registering everything) to install OS and software fresh... hopefully, you won't be one of those people
Read Bill Hunt on a file type as WRAPPER http://forums.adobe.com/thread/440037
What is a CODEC... a Primer http://forums.adobe.com/thread/546811
What CODEC is INSIDE that file? http://forums.adobe.com/thread/440037
Report back with the codec details of your file, use the programs below... a screen shot works well to SHOW people what you are doing
For Mac http://mediainfo.massanti.com/
Once you know what is in the files, you will know what codec you are missing