Can you open the .mov file in QuickTime Player and it plays? If so, qhile in Quicktime Player, type the letter i while holding down the Command Key. This will open the Inspector. Tell us the dimensions of the clip and everything you see next to the word FORMAT:
Then we can give you advice on conversion.
I think the issue is that iMovie cannot edit 60P. You will need to convert the HDV to 30P.
I think you could do this in a free tool called MPEG Streamclip, but I have not tried it with HDV.
Drag the clip into MPEG Streamclip. Then FILE/EXPORT TO QUICKTIME. Choose Apple Intermediate Codec as the codec and choose 30 as the frame rate.
If MPEG Streamclip does not work, I would try another free tool called JES Deinterlacer.
Once you have converted the clip to 30P, use FILE/IMPORT MOVIE... to add it to an iMovie Event.
If you want to keep your 60P footage, (because for example, you need to work with slow motion), then you may want to try Final Cut Pro X. I think there is a 30 day free trial, so you could see if it worked for you.