My macbook has random disappearing/deappearing dead pixels now that I've upgraded my ram?

Just upgraded my RAM on my MACBook from 1 GB, to 2.5 GB. I bought a 2 GB stick and Replaced one of the 500 meg sticks but now random dead pixels show up on my screen which disappear if highlighted or a window is placed over them but reappear in a different spot later. Also programs have been crashing. I bought PNY RAM from New Egg that says to be compaitble with Macbook and Macbook pros. Any ideas?