can't create a new layer???

So here's the story...i have this pic of me i was touching up. I made my eyes stand out more, fixed up my hair, and toned down parts of my skin that the flash had made over exposed. I also used an adjustment layer to increase some shadows and contrast. Simple enough, right? so i saved it as a GIF file, and closed out. A few hours later i decided i wanted to do some focal B+W work on it. So i go and get all ready to create a new layer for the parts i had selected to stay in color...only it wouldn't let me. Not 'wouldn't let me' as in my computer was being slow. no. 'Wouldn't let me' as in the option under 'layer' to 'create new layer' was unclikable...what happened?? with any other photo i pulled up, i could do everything. with this one, i could do NOTHING. what happened that won't let me do this??

Hi,
It was a big mistake - saving your work to GIF format.
First of all, a GIF image may contain up to 256 colors. All the other colors (about 15 millions) were lost for good.
Second, the "Indexed" color mode (used in GIF's) doesn't allow layers.

Now you can create a new layer in your GIF (convert it to RGB mode: Image > Mode > RGB Color). But all the previous layer structure is lost.

Resume: to retain the original quality and layers of your future projects save them to PSD format.