All of the sudden the Nano will not accept programming I have been working merrily along with CH340 to make Com10 work.  It has been working flawlessly but now I am getting various messages like it can't open the port then the programmer is not responding.  It tries several times before giving up.

This was working fine yesterday.

I tried uploading to a raw board not connecting to anything and am getting the same result.

Suggestions?
This problem occurs quite often with all the boards. Here is how to troubleshoot it.

1 - Unplug the Arduino.

2 - Upload the program WITHOUT any boards connected to your computer.

3 - Replug your Arduino.

4 - Upload the program WITH your Arduino connected to your PC.

If this doesn't work, read this post by Nick Gammon.