Installation Manager crashes to Desktop

I’m using the Steam version of the game. The Installation Manager kept crashing, like 20+ times. So i decided to do a clean install. Now it’s crashing installing the base game! No warning, the window closes with no error message.

I was hoping to leave the PC on over night to install, but this isn’t possible if I have to restart the Sim every 10-15 minutes!

…and now the PC literally just restarted itself mid-install. And now it’s stuck on ‘Checking for Updates’. Do I start installation from scratch again?