Slam to all... when I bought my computer I have 512 ram in it but when the ram damage I change it with 128 now when I put new ram of 512 the system cannot boot and stops on the starts of booting... what can I do please help me...

Check to make sure the speed of the RAM sticks is correct.

Check to make sure your ram is the same speed as the original ram and that the ram is properly seated. What OS are you running on 512mb?