Compression problem

Hello guys,

For the last two days I have been struggling to find a way to continue editing my documentary film, but haven't found a solution yet.

Some weeks ago I installed fresh version of OS 10.7.5 to fix some other issues (not related to FCP7) and now when I opened FCP7 to continue editing my recent project (which was stored in external hard-disk), but for some reason I couldn't open the timeline. It started to load and soon error occurred:

"codec not found you may be using a compression type without the corresponding hardware card"

Also, video files related to the project, in the "viewer" window only showed the green color, but the audio was fine.

I managed to get back the timeline, by changing compressor settings to "animation".
Now I can see the the timeline, but the timeline's video files seems to be un-rendered, and when I try to render, I get the same codec error.

But the green color in the "viewer" is still occurring when I try to preview the video files related to the project, However, if I add some video file which is not related to the project, then I can have a proper view of it.

I would be really thankful if anyone could help me with this.