If you are using Windows Professional or Enterprise editions, this may be caused by Hyper-V. You should disable Hyper-V when using Genymotion Desktop.
Please refer to Genymotion Desktop and Hyper-V (Windows Pro/Entreprise) for detailed instructions.
Your hardware does not meet Genymotion Desktop requirements
Check that your hardware and software meet Genymotion Desktop minimum requirements.
Please refer to What are Genymotion Desktop requirements?
Intel HD/UHD integrated GPU on Windows
Make sure to set your power settings to performance mode when using Genymotion Desktop.
Also, some laptops have a discrete GPU (NVidia/AMD) combined with an integrated GPU (Intel). In this case, you may need to force Genymotion Desktop (player.exe) to run with the high-performance discrete GPU (usually AMD or Nvidia) instead of Intel low-performance IGP. For more details, see How to force Genymotion Desktop use the high performance discrete GPU on laptops?
There are known issues with Intel drivers on Windows. If you are using this type of GPU, please refer to The virtual device crashes, freezes or fails to boot on Windows for more details.
You are using developer tools
Make sure that you set Genymotion Desktop to use the same SDK tools as your IDE. Please refer to Genymotion Desktop user guide.
The Virtual Device is too modern for your hardware
Virtual Device Android version and display density have a huge impact on performance.
If Genymotion Desktop is too slow on your computer, try a virtual device with a lower Android version and 320-XHDPI density. See What are Genymotion Desktop requirements? for more details.