My memory card isn't working?

I have a nikon D40, and my memory card is a 4gb. It had like 1500 pictures on it, and it was working perfectly, but today it said that it can't be used and may be damaged, but there's pictures on there i really need. How can i fix it? I don't even know what went wrong with it.

Try removing it again and replace it see if that will work or another thing you could try is; insert it into you PC or laptop to see if it can read it, good luck and if all else fails you could contact the manufacturer as sometimes they can attempt to recover, good luck

First, buy a $10 memory card reader for your computer and attempt to transfer the photos from the memory card to your computer.

Second, the reason you are having this problem is because you are using your camera WRONG!

Your camera and memory card are NOT intended to be a storage device! That is why it is possible to save photos from your memory card to your computer! The proper way to use a digital camera and memory card is as follows.

1) Move all photos from the memory card to a computer for safe keeping.
2) While the memory card is in your camera, use your camera to format the memory card. This will erase EVERYTHING on the card and will rebuild the card's file structure so that it will not become corrupted like it is now.
3) Go shoot pictures
4) At the end of EVERY DAY that you shoot photos, repeat steps 1 and 2 above.