Having problems with camera/SD card? Nikon d3100?

I have a nikon d3100.
I have a 16 gb.SD card in it! I've been filming and taking pictures with it for a while now and it never gave me a problem.
But today, for some reason it stopped taking videos.
It said card full, so I cleared the WHOLE card on my computer.

I inserted the empty SD card and it still said "card full."

So I JUST went to CVS and bought a new SD card (8 gb.)
and I inserted it in my camera.
Now it's saying "card is damaged and can't be used."
It's brand new.

What the heck is going on? I'm on vacation and I need my camera.

Never manipulate your card in a PC or Mac. Once you copy images to your computer from the card, put it back in your camera, and format the card in your camera. Get into the menu and choose the format option. Formatting erases everything so make sure you have copied your photos and video first.

You could corrupt your memory card if you do anything to it with a computer. Confirm that the safety or write protection tab on the memory card is not in the wrong position, it's tiny and easy to miss. That's all I have, hopefully you are not having camera issues.

Just to add to Sound Labs advice

For video in DSLR cameras a class 10 card is advised, anything below this can cause issues, exactly like what you described stopping while videoing.

Also the sensor can overheat during prolonged use - video isn't my thing so can't advise.

As Sound Lab advises try the Format option, and make sure your SD is class 10.

Hope you get sorted, Good Luck

To erase everything in the memory card, use format. It's an item buried deep in the menu system of your camera.

A new card that is damaged is probably fake. Buy memory cards only from a reputable store.

Always transfer your pictures and videos to your computer at the end of the day then format the card in preparation for the next shoot. Formatting keeps the card healthy and the camera happy.

For video, use Class 10 SDHC.

Sounds like your camera's card slot is broken. Look at the new card. Is it physically marked in anyway? The card slot could be damaging the card.

Try formatting the 16GB card in your computer, then again in your camera. That will sometimes revive the card.