System shows waves on screen

Hello, i m using windows 7 and i updated my ram 2gb to 4gb(two slut of 2+2gb) at that when i use system it shows waves on screen, i put off my new ram installed but problem persist. but when i put off my old ram 2gb it clear this fault. what happens at once even with my old 2gb ram even it was running or working good before installing new ram of 2gb. plz give solution for it