repair gamecube discs

[Marshall4]

All of a sudden my kids gamecube disks won't work - just gives message "Please insert disk". Only 2 that will work. I've cleaned them, they don't look bad, but won't work.
I tried using DataDoctor to clean the disk, polish and buff, but still won't work.

Could there be something wrong with the gamecube? (But why will it read 2 disks?)

Is it scratches on the disk (Then why didn't the one I cleaned work?)

Is there a special DiskDoctor that works better with the mini disks?

Any way to read the disks in computer and check for errors?