I've been working on a program for a week or so now with vMicro on a MKR1000 using the serial debugger and it's been working great. This morning I added  breakpoint to a constructor of one of my classes (maybe a mistake...). As soon as I did the upload the serial port disappeared from Windows never to return. I can put the board into bootloader mode and the bootloader COM port shows up (and the onboard LED pulses, which I assume indicates that it is in bootloader mode), but no combination of changing computer, trying to upload, reinstalling the Arduino IDE, etc. will make the main COM port responsive again to let me upload the code.

Any ideas or am I the proud owner of an Arduino brick?

Actually, made a bit of progress. I was able to get the blink example to load via the boot loader (I'd reverted to using the Arduino IDE directly which failed, but when I tried again in vMicro it worked), which restored the COM port and things seem to be roughly back to normal and if I delete the breakpoints in the constructors things work. Putting a breakpoint in the constructor does replicate the issue.

Thanks for the quick support, and yes I think that must be what's happening, the constructor is being called for a global instance of the class.

I coincidentally ordered up the Atmel ICE yesterday, so should be covered going forward.