Hi leeds-rover and welcome to Tom's forum.
What current RAM do u have? Remove the current RAM, install the new one and try again.
Thank you for your response! I am using the same as I mentioned above - 2 x 1gb of corsair ddr2 ram. I have tried the different ram in different slots and have mixed up the old and new ram and it works but only if there is no more than 2gb installed. I don't understand why it won't work!