Only half of installed RAM is working

[remember]

Windows xp home ed on Sony Vio notebook 2003. I bought this computer with 512 installed RAM. It worked fine until a few weeks ago when it slowed down considerably. I check the "RAM installed" and it stated 256. A week or so later the speed picked up and I checked the RAM and it said 512 was installed. (this was after removing real one player -- don't know if this was just coincidence) Great. But a week later I am back to 256 RAM

[Darkdrakon]

the first thing you need to do is make sure the mem stick is seated corectly. if that is not the problem take it out and have it tested at your local computer place.

[ozrensky]

... insert just the new one to make sure is working!

[Wesson]

I know you have to make sure your processor can handle it maybe that