If you are using a Windows PC, check this first (this list looks quite long, but the first three bullets will let you know if Hyper-V could be your problem, and the next five bullets will tell you if this answer will solve your problem - just a few moments!):
Open a good old-fashioned command prompt (not a PowerShell) with admin privileges and type:
bcdedit
Enter
Take a look for an item in the list called: hypervisorlaunchtype.
If hypervisorlaunchtype isn't in the list, or is Off, exit this answer and take a look at one of the other answers on this page.
If hypervisorlaunchtype is in the list and is set to Auto, Hyper-V is installed and is enabled.
Disable hypervisorlaunchtype by typing
bcdedit /set hypervisorlaunchtype off
Enter
Reboot
Try to start your Genymotion device again.
If it still fails enable hypervisorlaunchtype by typing into an admin command prompt:
bcdedit /set hypervisorlaunchtype Auto
Enter
Reboot
Exit this answer and take a look at one of the other answers on this page.
Otherwise, if your Genymotion device now starts, you have a choice:
If you don't need Hyper-V remove it by un-checking it in Turn Windows Features On or Off and exit this question.
If you do need Hyper-V, allow easy enabling and disabling as per Scott Hanselman's blog post, which I will outline in the following bullets:
You can leave the default as Off and then add an item to the boot menu that allows you to switch it on, or vice versa.
If you are leaving the default as Off type the following into the admin command prompt:
bcdedit /copy {current} /d "Hyper-V"
Enter
and you will get a response like this:
The entry was successfully copied to {ff-23-113-824e-5c5144ea}.
then type:
bcdedit /set {ff-23-113-824e-5c5144ea} hypervisorlaunchtype auto
Enter
(ensuring you swap the GUID for the one your call to copy above gave you)
Restart and then select Other Operating Systems on the blue screen and then Hyper-V on the subsequent screen and your OS will restart with Hyper-V enabled.)If you want Hyper-V to be enabled by default type into your admin command prompt:
bcdedit /set hypervisorlaunchtype Auto
Enter
(which will revert the default boot to enabling Hyper-V)
Then type the following in the admin command prompt:
bcdedit /copy {current} /d "No Hyper-V"
Enter
and you will get a response like this:
The entry was successfully copied to {ff-23-113-824e-5c5144ea}.
then type:
bcdedit /set {ff-23-113-824e-5c5144ea} hypervisorlaunchtype off
Enter
(ensuring you swap the GUID for the one your call to copy above gave you)
off by default above, in order to switch between the two hold down the Shift key when you go for a Restart and then select Other Operating Systems on the blue screen and Hyper-V on the subsequent screen and your OS will restart with Hyper-V enabled.)This comment and this answer to the question you are currently reading lead me to the resolution in my case and I am adding this answer to outline simple steps to take before you spend a lot of time on any solution - that comment and answer do get you where this answer will take you, but I have laid it out step-by-step in the hope that you can save time.
Background:
This article by Scott Hanselman gave me the meat of what I have outlined, with this comment on that blog post by Jonathan Dickinson helping with my background understanding and preventing me disappearing down a rabbit hole, but this article by Derek Gusoff fine tuned the steps above.