It says 240-pin fits but it's not. What am I missing? Obviously I bought the wrong RAM, but how do I know which 240-pin is the right one? Thanks.
More aboutwrong memory
You bought DDR3 ram instead of DDR2 which your motherboard supports. DDR3 runs at a higher frequency, different timings, and different voltages. Send it back and buy some DDR2 800mhz ram because thats what your board supports.
your motherboard supports DDR2 (800 in particular) and you bought DDR3-1333. They have the same number of pins but they aren't compatible and they have a notch in different locations so you can't mix it.