Internal screen doesn't work, external does

hello there,

not much can be deduced from your description except that the matrix does not work :-)

There are several options that should be checked, starting with checking the matrix with another working computer, checking the power circuit, display and backlight in the motherboard. However, everything is indicates that the signal tape of the matrix has been abrosed. You will find it under the macbook logo sticker. This can be soldered if the damage is superficial. If the tape has already been torn, unsettled, you will have to replace the matrix.

Alternatively, if You can't microsoldering a finding a proper repair service is good idea always.