Yesterday the launcher didn't react to clicking Play. I closed the launcher, retried with similar effect and then ran Repair and Repair failed. The repair process fails each time I try as it approaches full verification. It gives Error 1005. I have never encountered this before.
I have set the launcher to run as administrator, checked that all appropriate files are given exemptions by firewall and anti-virus, checked that WMI service runs - as proposed in similar cases here.