Micro disappears from device manager, Port grayed out

(This is a re-start of an old thread started in 2013, as suggested by Forum)

I am fairly new to Arduino & have a Micro. I am running Windows 7 Home Edition and IDE 1.6.4

A few days ago, I had no problem loading and running the given code for the MPL3115A2 air pressure/temperature sensor. (https://github.com/adafruit/Adafruit_MPL3115A2_Library)

Today, I find that when I load the sketch, the Com port disappears from the Windows 7 device manager. Consequently I cannot run the serial monitor, getting the message "Board at COM8 is not available." The Port selection (under Tools) is grayed out.

I found and followed the advice by hiduino (http://forum.arduino.cc/index.php?topic=153674.0), and found that I could work around the problem for simple sketches such as Blink by hitting the reset button just after compilation and before uploading. This does not work for larger sketches, it appears.

I have never selected anything but the Micro under Tools->Boards, avoiding a mistake hiduino suggested may be the problem in some cases.

I have seen no recent traffic on this thread, so I am hoping the problem has been solved and I just haven't found the solution.

Help appreciated!