rippled display usualy is a result in your video card and monitor having a time keeping in sync at the same display size, color depth, an refreash rate

check your monitors manual see what the aaverage refreash ( hertz) speed rating it lists for 1024x768 be sure its rated around 60 for that resolution

i have an older monitor only runs at 40 at that resolution and it won't run at all off my old mx 420 gforce card


other possabilities.

something is loose... video cable, video cards loose in the slot
failit fuse in monitor. or something worse in teh monitor is slowign failing