SD card isn't working properly now?

Its a 16Gb regular SD hc card. I've been using it perfectly for about a year now and its been great. But a few minutes ago I was sorting through some pictures I just took, and all of a sudden All of the pictures from the card were suddenly deleted. And they didn't go to my trash or anything. And it was sudden, they deleted AS I was previewing one of the photos. I did not bump the SD card ( I use an SD card reader) and the card is not in the "lock" position. And when I put the card back in my nikon D90 dslr camera, all my pictures preview fine. But now when I put it in the computer, it doesn't show anything and it just says it needs to be formatted.

The card has probably failed. These devices don't las for ever. By the way there's no such thing as a "regular" 16gb SD card. Anything above 2gb is SD HC, FYI.

I'd say it's time to trash and replace that card - it's probably done.

When was the last time you formatted the card? If you do not format frequently, the card will become corrupted. The proper way to use a memory card is as follows:

1) Transfer all of your photos from your memory card to a computer for storage (NEVER store photos on a memory card… They are not designed for that).

2) Format your memory card while it is in your computer following the instructions in your camera's owner's manual. Formatting the card erases all data and rebuilds the internal file structure like new.

3) Take photos.

4) At the end of EVERY day that you use your camera, repeat steps 1 and 2.

Http://keerok-photography.blogspot.com/2011/05/how-to-keep-your-memory-card-healthy.html

If it works in your camera but not in the card reader doesn't that give you a clue?

Either your card reader has failed or the USB port on your PC.

Do you have another card to try?