I put my gamecube game in and it says cant read

if the wii console is laying flat on the table/floor/wherever it is you use it, with the power & reset buttons on the left, open the flap on the left hand side of the console (hinged on the botton). You will reveal 4 slots for plugging in your controller

Well it might be that the GameCube is over heating then by the fan not working properly to help cool down the console so it will have to be fixed then

If the game disc is scratched, you can get it resurfaced at a used game store or movie rental store. If it isn't scratched, the disc might just be defective. It doesn't happen very often, but it's possible.

There have been a couple of flaws in how the Wii reads Gamecube games, so this could be for a couple of reasons.
1. Some games simply just cant be read on the Wii, but it is completely determined by the game...not the Wii. This is a flaw found in mostly Gamecube games and sometimes Wii games. I have heard of Super Smash Brothers Brawl not working on certain Wii's. In your case, with Mario Kart Double Dash, it could just be that the game simply cannot be read. If this is true, then there is nothing that can be done. (You can test this by putting the game in somebody else's Wii)
2. A more common problem is scratches or fingerprints. If this is the case, then get scratch removal at the store. If you don't want to, then toothpaste will sometimes work.
3. If all else fails...read the instructions booklet.

HAte to say it but I think the slamming may have permanently broken your console. This happened to my PS3 after it was jarred aroud too much. It would probably be cheaper to but a used Gamecube than to try and send it in to have Nntendo fix it. They're 29.99 at Gamestop used.

One time I ccidently touched the lens in my 10 year old gamecube so now the lens and the laser dont read the discs anymore because it is knocked out of anglement so you could buy a new gamecube now or buy a wii because wii's can still play gamecube disc's too.
Game Cube Disk Read Error Fix (Advanced Skill)

the discs you bought is damaged or some sort of data missing jst simply replace your disc

try cleaning you lens or cleaning your game disc.

did you check the back of all your discs for scratches thats the problem or gamcubes broken down if you try a new game and it does the exact same thing send your gamecube to nintendo for repair hope this helps.