I wanted to test out the W10 April update before putting it onto my main machine, and it seems I was justified in doing so.
I used my Lenovo ideapad 320 that was up to date with 1709 and let the update run.
Eventually, it seemed to finish and on logging in I got an error box "Location is not available - C:\WINDOWS\system32\config\systemprofile\Desktop is unavailable". Clicking OK resulted in a black desktop on which NOTHING would work. I could get a Run window up but couldn't get anything to run. I could not get the Start menu to work, so the only option was to turn off the machine. After about four reboots I suddenly got the normal desktop but after a couple of minutes suddenly go that error box again.
I gave up for the evening and when I tried this morning I got the expected desktop. BUT, things are still not right. The Start button still doesn't work. Using File Explorer to find certain programs, but practically nothing would run. I cannot access the Internet as while I can click on the network icon, 'Troubleshoot problems' works but 'Open Network Internet settings' does not.
Suggestions as to what to do next would be greatly appreciated.