You didn't mention in your attempt to read the card with your computer, whether you just plugged in the camera via USB cable, or tried to read the card using a card reader. If you don't have a USB card reader, get one and try to read the card that way. They're very inexpensive, here's an example:
http://www.amazon.com/Transcend-Flash-Memory-Reader-TS-RDP5K/dp/B001NS828K/ref=sr_1_1?ie=UTF8&qid=1309123515&sr=8-1
If you still can't see the files with the reader, your next attempt should be to use recovery software with the card reader. There are very freeware options that you can try before considering the payware route. Here are a few:
http://camerarepair.blogspot.com/2007/12/recovering-those-accidentally-lost.html
Finally, after recovering and saving your photos to your computer, now format the card IN YOUR CAMERA using the camera's format feature. This should rejuvenate the card to good as new, but as you're aware, it will also erase the card.