itunes wont play songs that weren't bought from itunes

when my mom opened up itunes a contract popped up and she clicked the i agree button. I don't know why but itunes now won't play songs that i have burned from cds. An exclamation point pops up in the column furthest to the left. a box pops up and says, "The song ______ could not be used because the original file could not be found. Would you like to locate it?" What should I do?

thanks in advance