Remember the old expression “If Mama ain’t happy, ain’t nobody happy”? Well, if your hard disk isn’t happy, iMovie won’t be happy, either.

Here’s a short list of maintenance suggestions. A little attention every week or so may help keep minor hard drive problems from becoming major ones:

First, note that some camcorders refuse to enter PC connection mode unless you plug them into a power outlet. They won’t even consider entering PC mode when running on battery. (The camcorder’s fear is that it will run out of battery power in the middle of the transfer, possibly corrupting and ruining some of your video scenes.)

Next, try plugging the USB cable into one of the USB jacks on the Mac itself, rather than into the USB jack on the Mac’s keyboard. (The one on the keyboard is for low-powered gadgets only.)

If you double-check these conditions, quit iMovie and reopen it. Now, at long last, the Import screen should appear.

Try these checks, in this order:

Make sure you set your camera to VCR or VTR or whatever the setting is called that plays back your tape. Check the FireWire cable connections. Turn the camcorder off and then on again. Quit iMovie, turn the camcorder on, and then reopen iMovie. Restart the Mac. Try a different FireWire cable.

Do you have a high-def tape camcorder (one that uses the so-called HDV format)? If so, delve into the menus and make sure that the camcorder’s output matches what you recorded.

See, these camcorders can record either standard-definition or high-definition video on the same tape. But when you connect the camcorder to a TV or a Mac, it has to know which format to transmit.

Usually, you get a choice of DV (which means standard definition, 4:3), HDV (high definition, widescreen, 16:9), and Auto. But Auto doesn’t always work. If you’re having problems, choose DV or HDV manually.

You know the cool iMovie Preview window (From an iPhone/iPad/iPod Touch), where you get to see and even play the thumbnails for the video on tapeless camcorders before you actually import any video? Sometimes that preview playback looks awful. It might be jerky or have nasty interlace lines, for example.

Rest assured that this is all just a problem with the preview. Once you actually import this footage, it’ll look fine.

If you’re used to the old, old iMovie, you might wonder why you can’t hear anything as you import footage from your tape camcorder. That’s because iMovie no longer plays audio through the Mac when you import. If you want to hear the soundtrack as you import, leave the camcorder’s screen open so you hear the audio from the camcorder itself.

If you can’t even make it past the startup phase, you can try deleting iMovie (just drag the app to the Trash) and reinstalling it from the Mac App Store. Don’t worry; deleting the app doesn’t delete all your movie files. Those are stored elsewhere.

Also consider rebuilding your iPhoto library; iMovie checks in with iPhoto every time you open it, and if there’s something wrong with your iPhoto library, iMovie chokes. To rebuild the iPhoto library, quit iPhoto, and then reopen it while holding down the ⌘ and Option keys. In the resulting dialog box, you see several diagnostic options. Choose the Rebuild button, and then wait a very long time. When it’s all over, iMovie should be much happier about doing business with a clean, fresh iPhoto library.

See the Note on Note.

A dropout is a glitch in the picture. DV dropouts are always square or rectangular. They may be blotches of the wrong color or may be multicolored. They may appear every time you play a particular scene or may appear at random. In severe circumstances, you may get lots of them, such as when you try to capture video to an old FireWire hard drive that’s too slow. Such a configuration may also cause tearing of the video picture.

Fortunately, dropouts are fairly rare in digital video. If you get one, it’s probably in one of these three circumstances:

If you spot the glitch at the same moment on the tape every time you play it, then the problem is on the tape itself. If it’s there during one playback but gone during the next, the problem more likely lies with the heads in your camcorder.

If you open the iPhoto library and try to drag an iPhoto photo into your movie but you get a “The file could not be imported” error message, you’re probably working with a RAW image file. (That’s a high-end photo file format created by semiprofessional SLR cameras and intended for processing later on a computer.)

The solution: Return to iPhoto. Make a tiny change to the photo, like a small crop or brightness adjustment. When you exit editing mode, iPhoto applies the change and, in the process, turns the RAW photo into a JPEG or TIFF format photo, which iMovie can import.

Yep, you can’t use an audiobook as an iMovie soundtrack. They show up in the Media browser, all right, but if you drag them into iMovie, nothing happens. Them’s the breaks.