iMoviHD: Video FX not applying!

[MalcolmO]

I recorded a B&W movie that requires changes in Brightness and Contrast, but the Video FX will not apply. From the whole effects list, only one --Fast/Slow/Reverse will apply! All I get is a "blip when I click "apply" and the button immediately is again "active". No rendering line in the clip -- nothing. Apple help says remove 3rd party plug-ins from the QuickTime file which I did, but no improvement. On other files, the effects will apply, and I have even moved the movie to another HD -- no good. I then converted to QT "Full Quality" then converted that back to an iMovie file -- still no good
Would appreciate any help-- I've been working on this for days
Tks
Malcolm