Asus X550Z , "Preparing Automatic Repair" then blank screen
Start your Asus Laptop, then just after the Asus logo disappears and Windows 10 tries to boot, press and hold the power button down for 5 – 10 seconds to perform a hard close down down
Do this Twice
On the third boot attempt, Windows will boot into the Windows 10 Repair Environment, from there you can access Activate Recovery, Safe Mode, Command Prompt . . . etc.
Try going to Troubleshoot – Advanced Options – Method Restore to see if you have a recent restore point you can go back to
If not try Troubleshoot – Advanced Options – Activate Repair
I Hope this Helps!