All you have is 2G or ram there bro. You have 4 sticks. What you have is 4 512 sticks that equals 2G.
You bought the wrong kit for 4G, you should have:
Patriot Signature Series 2GB (2 x 1G) x2 or
Patriot Signature Series 4GB (2 x 2G)
Your sticks are 512MB, put only one in and look in the bios, it will say 512.
The first clue should have been the price:)