Helmet Cam - iMovie Import Issues

Not the New Year post I thought I'd be posting but I'm asking for help here.

I cannot import any cam video into iMovie, haven't been able to import since about September 2012. This makes editing them and making them into race clips impossible.

The files get put onto disk - I've used 500GB of drive space trying to import the White Plains cam clips - but there are no files in Finder, no nothing. Until about November I could see the file in Finder under iMove Events, but now no files show up.

I tried another race (a Rent) and that didn't import either.

I tried renaming the file (copy and rename) I want to import. I tried putting it on a different drive (internal, external-1, external-2).

There is enough space. I started with about 800-900 GB free - so much that I forgot the exact number Now I'm down to ~350GB free on my 1500 GB drive. As an FYI each 3.94 GB cam clip becomes 32 GB raw data in iMovie, before any editing. Finished clips, typically 8-10 minutes long, max 15 minutes, take up 50-100 GB each, and I think one is 200 GB (that's actually a shorter clip but I split the audio off the video).

Any Mac guru suggestions welcome. I am Mac illiterate for all intents and purposes.

I have a 2 GHz Intel Core i7 MacBook, OSX 10.7.5, 16 GB RAM, 500GB internal, two 1.5 TB externals, two 2.0 TB external backups (one for each 1.5 TB). I can no longer use external-1, a 1.5 TB drive, as it's has only 700 MB free, I think due to multiple import attempts. External-2 is down to 380 GB and the last 5 or so import attempts have used drive space but has produced no visible files.

My next steps: I will add another external drive (2 TB) and see if using a clean drive helps. I'll dismount the four other external drives as well. I'll try and split the file into two so that it's about 1.9 GB per file.

I've really wanted to work on clips but the import process takes a few hours and I haven't been able to babysit it and see if it errors out.

As soon as I fix this problem I'll be producing YouTube clips again.