Why does all the photos I import from my camera gets copied on to my pc twice?

So, everytime I import photos from my Nikon D40 to my pc, whether I stick the memory card directly into the pc or use the usb cable, each picture is imported twice. And the second copy of the picture can't be used for anything (Can't be edited on any program or uploaded on the internet) This is very annoying because I have to delete the second copy of each picture and stuff. Anyone knows why this is happening and how I can prevent it?

Sounds like you might be saving each photo you take to the camera as "RAW and basic JPEG"
This will save two separate images to the memory card each time you take one photo.
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You can check this easily.

Turn on the camera and press the MENU button.
Scroll down to SHOOTING MENU and highlight IMAGE QUALITY.
It should say FINE in the right-hand column.
If it doesn't, right-scroll and change it to FINE

RAW images sometimes require further software or plug-ins before you can edit them.

This is based on the information you have given.