why do I lose the format of my webpage when I design with dreamweaver?

I have downloaded a free webpage frame to build my personal site. I have started adding information but at a certain point the webpage I have created loses all formatting (colors, tables, shadows, borders, etc) and becomes like a white page with paragraphs with normal sort of word formating… what´s going on? I though I had done some mistake without noticing and started again from scratch… and now it has happened again!! help!

Make sure your style sheet (the file that has extension .CSS) is in the same place that is pointed in your pages between the <head></head> tags after you save it in dreamweaver.