What cables do you use to connect the Wii to your tv? It might be just something wrong with the cables instead.

Seems like GPU and/or VRAM damage, more probably the second. Try checking the cables too.

Here another thing you can do, try connecting another system to your TV. If you get the same black lines it might have something to do channel used to play games ( game/video1&2 etc.)

I´ve read about something similar, if you have the same problem i´ve read about then sending it in and having it fixed is the only way.

I hope you gfigure it out.

It might have gotten overheated somehow. I didn't say it in my first and second post because usually an overheated GPU result in color distortion usually greenish not black. If that's the case then you'll have to send it in to Nintendo to get that fixed.

I thought my N64 was broken once but if was because of bad cable connection.

First pull out the cables and plug them all back in and try again.

second try pulling out the seperate cables from the scart adapter [I assume you use it] and try again.

third try another system into the same ports to make sure its not a TV fault.

fourth call Nintendo.

(fifth: profit!)

Just use a little effect-to-cause:

1. Try it on a different tv

2. Try borrowing someone else's video cable

I thought my PS2 was fried once, only to find out the input connector on my TV went bad.  It would have been cheaper to replace the PS2. :-/

Take a picture?

dude, you must have dropped your wii by accident! my wii fell down off my tv yesterday and this has been happening to me all morning! (i was playing moh:h2 and i accidentally did the grenade gesture and knocked my wii down. everytime i put a game in it would come out. that part of the problem has been fixed though.)

Sorry I misread that part. Are you sure that this is just a Wii problem? you should try connecting another console to the TV and see if it has the same problem.