Memory New memory

hi i have just got some new memory http://www.scan.co.uk/Products/02GB...800)-240-Pins-Non-ECC-Unbuffered-CAS-5-5-5-18, to add an extra 2gb of memory to my pc. i've already installed it into my pc and it's not showing up when i switch on the pc but wehen i go into windows 7 it shows but is not being used. my question is how do i get windows 7 to use it

thanks in advance

 

this is what windows is showing.
when i boot up my pc the bois only shows 2gig