I had tried running as admin but that didn't work for me. What did work in the end was to reset my default browser to Internet Explorer. I normally use Opera but after that, it installed fine. I did notice, even though I already have Steam and it says, "Steam software found", it acts like it's installing something but just sits idle. Once I plugged in my Vive headset the installation completed fine. Good luck and see y'all out there.