A summary of the thread so far:
- The PCs which had a 3rd party Antivirus installed and did an upgrade to the latest stable release called April Update...
I don't know if this is usefull information or not, but the same problem happened to my bosses laptop (Lenovo B50), it only used the Windows Defender...
I'm a software developer (currently not woring in my field, so thats why I had to check it out), so I know what I'm talkin about. My boss said she didn't have to choose keyboard language, and it doesn't ask to select a voume for booting.
All it does is that it takes much longer to load in, then the black desktop, error message, etc. the usual things that everybody experiences.
It may be important (or not), there was a modification made to Windows, one of the users desktop (or the whole user folder, my boss didn't know) was relocated to D:\ (same HDD only partitioned).
I hope that this information helps finding a solution sooner.
(Sorry if my english is bad, not my first language.)
Tl;dr:
Same problem, no 3dr party antivirus even installed.