I have used adb reboot umpteen number of times earlier, with absolutely no issues. For some reason this time however, adb reboot simply freezes my Gennymotion emulator instance (API 18 - Android 4.3) and I have no clue how to solve this issue. I tried looking through logcat while doing adb reboot, but that did not point to anything interesting unless I have missed out something. Can someone please help ?
Another pointer, in case it helps is my emulator device keeps prompting that Google Play services has stopped working. During my earlier trysts with Gennymotion and adb I have had this issue a couple of times and just updating all of the Google apps had worked like a charm in the past. However, this time even this doesn't seem to be working.
Are you sure that the version of Google Play Services matches your API? Also, try to reboot your emulator by using adb shell reboot instead of just adb reboot.
If you have multiple devices running, you can run the Genymotion Shell and type devices show. Write down the IP address of the device you'd like to reboot. Now you can connect to the specific device by using adb connect ip[:port] (where :port is optional). After you've connected to the device of interest, you can execute adb shell to enter the device's shell or adb shell <command> to execute the passed command only, and then exit the device's shell immediately.
To install the appropriate version of Google Play Services on your emulator, please consult this website.