Dslr suddenly taking low resolution photos?

I have a nikon dslr camera which has always taken great pictures but today for some reason the resolution was very low on the pictures i took a few hours ago and i'm so disappointed! I hadn't messed with any of the settings or changed the resolution.before the dimensions on all my pictures were about 4, 000 x 3, 000 (rounding a little) and now they're like 500 x 400 D: can anyone please tell me how i can fix this! Or make the quality of the photos i took higher? I really don't want this to happen again, i don't understand it happened in the first place ugh.

I guess you have not read your user manual that discusses image resolution.

Since you did not tell us the model number of your Nikon, there's not any way for us to direct you to a specific page to help you

If you had a Nikon D300 you would find that information on pages 56 and 60

Look in your user manuals index under "Image Quality" and "Image Size"

I use SanDisk Extreme Class 10 SDHC cards.

A setting was changed. It may just a button you unknowingly touched. I'm guessing it went from best to ugliest. Read the manual on how to change resolution or picture quality. On my son's D50, it is just one button and a turn of the wheel to go around the numerous different image quality choices Nikon offers.

It sounds like accidental user-error in the menu, something that is very easy to do if you are thinking fast when changing settings. Sometimes if another person gets at the camera they will change random settings too. Always with your first shot of the day check the settings data on the most information-rich mode of viewfinder (LCD obviously if there's no EVF). I call it a 'flight-check' and it quickly becomes routine.

Sadly you can't get image detail back into shots that were too taken at very small size. The best you can do is manipulate edge contrasts with USM in Photoshop. (set Amount 38, Radius 12, Threshold 1 for local contrast) and then add medium normal sharpening. This will give you back a 'snap' photo look.