There is only one white fuse box?

There is only one white fuse box located under my spare tire under the foam mat. It has gotten wet and my car has gone completely without electrical power. There was a lot of water in my trunk and I don't know how that occurred. When I lifted the fuse box, which has a lot of wires attached I noticed some green gunk on it. I have dried it out and attempted to clean it up. I opened the white box and sure enough it was wet inside. How do I remove the box and How do I replace it? Also, Is there another box somewhere that is hidden? I am stranded without another vehicle and financial resources are extremely limited. I am reasonably intelligent and if it can be fixed without special tools, I can do it if I am given instructions. Thank you, Susan