Male - 24 Years Old
Well unless you're using 64bit Windows XP then the operating system can only detect 4GB of that RAM. Seriously, fuck all this and just upgrade to Windows 7 64bit. It's not even that different from XP. You are running an extremely outdated operating system on a very modern system. If you have files on the HDD that you need to recover, you can remove the HDD, connect it to an external HDD enclosure and browse it on another computer. If not, fuck this noise and go straight to 64 bit Windows 7.
EDIT: Oh, and also - run the checkdisk like it tells you to.