Hi Collette,
What you are describing is a message that says you have run out of disk space for any more files.
Think of it this way, when you go shopping, you can only put so many items in your shopping bag. If you wanted to fit more items, you would need to get a bigger bag. This is essentially what has happened on your computer. The size or quantity of data of your video clips have exceeded what your disk drive can hold.
In short, you have run out of bag space for your items. In order to solve this, you can do two things. Delete things off of your hard drive to make space for other files, (not such a good idea because you'll run out of space again,) or have a computer savvy person add a larger capacity disk drive to your computer or swap out your old one for a new one.
Adding a new drive is the easiest way. External disk drives are readily available for sale now and you can purchase a 250GB drive for less than $120 in most cases. If you know a computer geek, he/she can add an internal disk drive to your computer if you don't want an external disk next to your computer.