Windows 2008 R2 VM (Hyper-V) won't boot after expanding primary VHD Disc.

I expanded C drive of Hyper V VM using helper VM and after that VM doesn't boot.

Solution: Attach Windows OS disc to VM and boot from it. Select repair option and then command line.

#CD recover

#bootrec.exe

This will restart VM and hopefully make VM bootable. In my case Bootrec was able to make VM bootable, but one applications was unable to start and was asking to activate it again.