I think there may be something wrong with my wii gamecube memory card slot A,
I put it in, something flashes for a second, but then it says there is nothing inserted, i know it's not the memory card because it works fine in slot B but not in A. What should I do?

Blow into it.It could be just dust thats causing it not to work.

But whats the big problem if it works in B?

As i sad give it and blow and it will probably work. :p.

Some games only work with slot A, so it is a problem if only B works. Like SSBM only loads data from slot A, I think.