You have two modules.. Both are 256 and both are in the computer (I'm assuming).
This should give you 512MB total.
If you already had 256MB that came with your computer, but added another 256MB and are only showing 240MB total, your new memory does not work in your system.
If you bought two new 256MB modules and only one is working properly, then one of the modules is likely defective (if they are the same brand). If they are different brands, then one either doesn't work with your system or one doesn't work with the other memory.
While the memory (even though new) can be defective, it is far more likely the memory is simply not compatible with your system or your existing memory.
To avoid this, it is best to buy high quality, name brand memory. The more you pay, the more likely the memory is to work in your system (by general rule of thumb). As manufacturing processes & methods advance and become cheaper, newer memory will not work with older systems as well.
Manufacturered computers are very specific when it comes to what kind of memory they like.
Keep in mind 256MB will show up as 240MB because of your onboard graphics, like Mic mentioned. As 512MB will show up as about 496MB. 16MB is dedicated to graphics.
alright thanx a lot for your help guys. Im gonna see if its compatible cause the one that came with the comp. was a 256 and it was pc133. So i got another pc133 thinkin that it would recognize it but i guess not.