Why is everything saving to notepad?

Iam not the most savy person with computers, any help would be greatly appreciated! ......my problem is, that almost any file i save is for some reason being saved in notepad form, even files with images and graphics are somehow saving in notepad.......now the problem is if its a larger file that notepad cannot handle, it will save it to notepad anyway, and when i try to open it, a dialogue box appears that says "this file is too large for notepad, would you like to open with microsoft word?".....so i click "yes" and then the file opens in microsoft word but is encoded........does anyone know what i can do about this?....is it something in my default settings??.........any help would be greatly appreciated!!