I assume that you are using some program to download the video to your computer.

Try it without using a program.

I have a Canon A570-IS camera.
I connect the USB cable to the camera,
then plug the other end of the USB cable to the computer.

On the computer I go to "My Computer" or "Computer" on Windows 7.
That shows me all the storage devices on my computer.

Now turn on the camera and put the camera in "playback" mode.
That is the mode you use to look at photos in your camera.

On the computer you should see the camera show up on "My Computer".
My computer shows a new storage device called Canon PowerShot A570 IS.
Double Click on that and then I see "Removable Storage".
Double Click on that and then I see "DCIM".
DoubleClick on that and I see 100 "Canon".
Double Click on that and I see photo files in the camera.

You should see your video file.
It will be a file that ends with .avi (i.e. xxxxxxx.avi)
That is your video.

Now look at the left side of the computer My Computer window.
Click on the tick-mark to the left side of your Computer C: disk.
Find a folder that you want to use for storage of the video file.

Now back to the right side of the window.
Right click on the video file name and drag it to your computer and drop it into a folder on your C: disk (left side of the window).
The computer will reply: Copy here or Move here.
Choose Copy here.

It will take a long time to download with such a large file as you have.