why not? i'll tell you what most likely the problem is
on your monitor you were using a resolution that is not supported by your TV (like 1280x1024 if your Samsung is like mine)
you just unplugged the VGA cable from you monitor and plugged it in your TV without changing the resolution back to something like 640x480 (or 800x600, something your TV supports) in the dashboard settings
if that's the case, plug your 360 with the VGA cable in your monitor, switch the res to 640x480, plug the 360 in your TV and change the res to your TV native resolution
otherwise post more infos