First of all try putting the card in a reader and see if you can view the images, if you suspect you erased the images there is software that will allow you to recover the lost images. Depending on the brand of card you use or used.
Here is a link to the Sandisk website, and it should open on the page for Rescue Pro, there is a Pro Version and a Demo Version. Some of the higher end memory cards come with a key code to unlock the pro version. You can try to use the version you wish to see if you can recover you images if they are lost.
Stoopid question are you or have you attempted to load the Nikon software that should have come in the box to download the images to your computer ? If not that is worth a try. Hope this helps you.
I don't know about other models of cameras but mine will count(number) photos untill 9999 is reashed. I know that I can use folder, but I don't for simplicity. I have shot above 600 photos during a photo shoot without using folders.
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