What do you mean "Its not seeing it"?
Does it show around a hundred megabytes less than 1 gigabyte?
This is a common issue. There is nothing to worry about. When yuor computer first loads, it loads something called the system dump. This is the data that runs the computer itself. It can take a large variety of RAM. Also, if you are using a video card that uses shared memory, you may have this problem. If you really wanted to, you could make up for the lost RAM by buying more, but its not nessasairy.
(* sorry, I dont have spell check right now)