IMovie 11 projects no longer working, preview window is glitched or black, event library not playing imported vids

Question

I am having a lot of trouble with iMovie 11.  I bought a new MacBook Pro 15" for the sole purpose of editing surgical videos for work.  iMovie 11 was working great initially for me (taking full length surgical video - up to 2 hours) and editing these down to anywhere from 5 to 30 min videos highlighting crucial steps for the surgeries along with transitions, ken burns, etc  (with the plan of overlaying narrative voice-over later).  I had about 15 of these videos edited sitting in my Project Library and multiple imported videos (dvd to m4v via handbrake then imported via iMovie 11) in my Project Library.  Now none of my projects play in the preview window, it's either black or a weird glitchy picture (like messed up pic of my doc or desktop... really weird) and only about 2 of my imported videos play in the project library, otherwise they are just black when I roll over them.  My projects are still intact as far as edited clip lengths and transitions, but nothing plays, even in full screen mode.  I tried making a new project and the imported video shows in the event library but when I add it to a project it's black (but does play in full screen mode, but impossible to edit this way).  I think the audio is actually intact although i'm not positive because these videos don't have any audio (there's some baseline level that fluctuates on the audio bars). 
I tried finalizing and exporting a project as an m4v (one that was a combination of two edited imported videos - one of the source imported vids working in the event library and the other not working) and the first half is all glitched up with no surgery video, but the second half is there with the transitions and everything (the half that is working in the event library).  This part does not show up when I am trying to edit the project. 
fyi - I had deleted some of the videos from my event library to unclutter a little some time ago, the projects were still working after that.
I can find all of my imported videos (in .mov format) that should be working in the event library when I look in the folder:
users/me/movies/iMovie events
If someone could please help me resolve this issue, I would really appreciate it.  I put a lot of work and time into these videos and it would be near impossible to start from scratch (which would probably be on some other movie editor like windows movie maker since my iMovie is not working properly even for new projects).  I'm hoping this is just some sort of glitch that can be fixed and my projects are still salvagable.  I can't remember if this started after I did a system software update or not.  This will be a huge dissapointment for me in the Apple platform if I have to scrap my projects because I had just switched over from the PC platform. 
I even got Norton antivirus and internet security to make sure I don't have some sort of weird virus.
I have a Feb 2011 15 in MacBook Pro 2.2 Ghz, 4 g RAM, 750 g HD, 1 g vid card.  iMovie ver 9.0.4.  Lion 10.7.2

Answer 1

Did you by any chance upgrade your Mac OS from version 10.6 (Snow Leopard) to 10.7 (Lion) during the time you were working in iMovie on all these projects?
If not, start by deleting the iMovie Preferences file.
Go to the Desktop
Hold down the Option key and choose the Go Menu > Library
Go to Preferences > com.apple.iMovieApp.plist
Move the .plist file to the trash and restart iMovie
See if the Project files react any differently. Failing that try doing a Repair Disk Permissions:
Restart the Mac, hold down the Option key continuously until 2 hard drive icons appear
Choose the Recovery Volume as your startup disk and let it run until you see the Desktop
Choose Disk Utility from the Recovery Menu
Run Repair Disk Permissions in Disk Utility
Reboot the Mac and when you see the Desktop appear launch iMovie
See if the Project files are the same or different. Next step after this is to one at a time take the Project folders out of users/me/movies/imovie projects. Move one to the desktop and start iMovie. Try skimming the projects that acted up recently. Moving one project at a time might help isolate which project may be causing problems. You can also place project folders back in their original location after doing this testing and iMovie will recognize them on the next relaunch. It won't hurt anything.