When I start a multi-core virtual device in Genymotion, I get this:

Wh
This is common issue faced by many developers for me this issue is raised when i create genymotion device for android version 5.0 and above versions here is the solution
For ubuntu
During startup, quickly press F12 or F2. Click on setup.
Using arrows, navigate to Intel Virtualization Technology. ( It might on the next page)
If it's disabled, then Enable it using arrow and enter key.
List item. You'll find "Save and Exit" written on top right corner of the screen.
Now start Your system and start genymotion It will work.