Help! How can I recover files from my broken Sony Xperia Z3+?

Help!

My Sony Xperia Z3+ is water-damaged and the screen is black. Computer makes "connecting-sound" when I connect the phone, but it does not pop up on the screen. It does though appear as a connected device called "android" (not phone, but as a "USB mass storage device"). I am not able to access this device, probably because my phone is locked (with a pattern code). Have tried to download several "Android Recovery"-softwares, but looks like I need to have enabled usb-debugging-mode or something, and I haven't.

After some research online I ordered an otg-cable, but I'm not really sure if it unlocking it that way is going to work, because the screen is black, and the phone is practically dead.

Is there any way I can get my pictures??? Some way of enabeling usb-debug from the computer?

Kind of desperate. Any help is appreciated!