check your device manager when you plug in your tablet. See if you get any questions marks(Other devices)... Also check your USB controllers, see if you find the tablet there.
try only the 1gb stick in the laptop... you could have incompatible memory sticks (will not work together)
From the net, I believe this laptop only supports 1gb max memory. not sure if 2x512 or if 1x1gb will work.