Signal strength drastically fluctuates.

I could use a little help with my wireless signal strength. I read the faqs and did a search but i couldnt come up with any answers. I use my wireless to connect my xbox to live. My router is in my office, my xbox in my room (two rooms, maybe 60 feet away). At certain times my signal strength will indicate full (5 bars or whatever it is) and at other times it will be only one bar. I thought it was from 7-10 at night, but now I notice it fluctuating again today so it seems to be more random than I thought. What could be some possible reasons for my signal strength fluctuating like that? Thank you for the help.

I did play around with that a bit and it didnt seem to make a huge difference. I managed to get my signal a little better by moving the various antenna's around, but when i try to stream netflix it now comes across very slow so i'm starting to think it may be an issue on their end. I am going to try out some of those things that you plug into the wall and plug your cat 5 into and see what happens.