Galaxy s6 internal screen is cracked and the phone wont turn on.

[AC Question]

I have both screen protector and a case covering the phone.
The 'inside' screen is cracked but nothing else is.

Not sure what to do or how to get important files out of phone.

 

[Rukbat]

You get the screen replaced by a repair shop willing to work on the phone without doing a factory reset first. (Most won't.) If the screen isn't working you can't communicate with the phone, so you can't get files from it (which is why all important files should always be backed up - you can't "recover" files from a lost or destroyed phone).