You probably have the "wrong" screen resolution/refresh rate selected, e.g. PAL instead of NTSC or vice-versa, or progressive-scan instead of interlaced, or some such.
If that's the case, then fixing it is, fortunately, easy. Boot it up, get the "rolling screen", and then press the "Change Video Out" button on your remote control over & over until you *can* see the screen. Then, you can set the output parameters in the Showcenter's setup menu.
There's probably a passage in the manual that explains the remote control buttons if the "Change Video Out" button isn't labeled on your controller. (On my controller, the button has an icon that's a rectangle with a right-facing arrow pointing out of it).
BittMann