Why does the picture go off center when connecting my hdtv to my laptop?

I've just bought a lcd tv(LG 32LG3000) whn i attach it to my laptop via the vga lead it starts off fine but aftr a second or 2 the picture moves to the right of the screen. It moves so far over that i cannot fix it with the tvs screen positioning. if i reset the tv it displays properly for a few secs the goes off to the right again. if the tv is attached to the pc via s-vhs it works fine but the picture is at a lower resolution and i want to make use of its hd functionality