How to get my camera to shoot at a higher resolution?

I have a Nikon D3000, and it has always taken photos at a resolution of 300. For some reason, today, when I took some pictures and put them on my computer the resolution was only 72.It was very upsetting because I need these pictures to be resolution 300 for a project I'm working on. Does anyone know how I can make my camera shoot at a higher resolution?

The 72dpi is just what your monitor is capable of showing. If you look at the actual dimensions of your image it should be very large. Something like 44 inches by 66 inches for example. All you need to do is change it to 300dpi in your editing program and you will be all set.

ISO 100 or 200

The number you are looking at doesn't matter a bit. Your image is composed of the same number of pixels it was composed of before, nothing has changed.

Don't even worry about that number until you are ready to print… And unless you are doing something odd, not even then. You tell the printer driver the size of your image on paper, and let it do the rest.