Have you tried manually changing the sequence settings to match the clips?
Also you're using a very old computer and HDV is a very taxing format to begin with. You might consider transoding the material to prores for your edit. If you decide to go this route, do a test with a few clips to make sure this format will edit smoothly on your system.
And what kind of drives are you uising, how are they connected and maybe most importantly, how many angles are there in your multiclips?
to change sequence settings, make the timeline active and hit command-zero.