Most buttons are not working

A friend came to me with his broken 3ds, it turns out his a,b,x,y,l,r,start, and select buttons arent responding same with his d pad, circle pad, and touch screen ( and it may not be reading his SD card anymore but that's still in question). His zl, zr, and control nub are still working though. In thinking a connection may have just gotten loose and told him Is try to fix it, but I want to figure out the problem before I open it up, can anyone help?