I hope I can help!
Now, without knowing exactly what kind of ram you purchased, I cannot tell you for sure what the problem is, but this is the most likely, and most common problem. That is to say, your computer probably does not support whatever kind of RAM you purchased for it.
There are Multiple kinds of RAM (DDR, DDR2, DDR3 - not including older variations), and many different speeds. Each motherboard in every computer can run only certain kinds of RAM, and supports certain speeds. Sometimes a motherboard will support multiple speeds, but some are more limited.As far as the type, most motherboards will only physically support one type, so that should not be a problem as any other kind simply should not fit. Looking at the specs of your computer, it is also possible that your computer limits the size of a stick of RAM that must be placed in each spot (It looks like you cannot have a stick of less than 2 gigs in any spot). That is probably not the problem as you purchased 2 gigs of RAM. It should also be noted that your computer supports a maximum of 4 gigs of RAM.
All of that being said, the most likely problem is that you accidentally purchased the wrong speed of RAM. Looking at the specs of your computer, the only speed it supports is DDR 2 PC2 - 6400
. It would probably be best to return the RAM your purchased and get some DDR2 PC2 - 6400 RAM. If this does not describe your problem, or if there is more to it, please ask!
I hope that helps!