Access Z5 compact that won't allow login

Phone overheated on holiday while videoing, warning message then shut down, couldn't restart phone pressing on/off button. Let battery die, re-charged, had to use volume up button with on button to re-book. Goes through Android start up and default start-up graphics, as soon as it gets to login screen it shuts down straight away. I need to get photos etc off internal storage - thought they were stored to external memory card, but must have forgot to set when switched to this phone in January from my old Z1 compact. Downloaded Sony PC companion software but won't recognise phone when connected via USB presumably as phone locked. Any ideas how to get stuff off internal memory card - short of de-soldering it and putting in another device! Help, Andy