This can happen when your graphics driver not working properly

Ways to fix graphics driver

One

Because of hibernating your PC long time graphics driver won't work

Shut Down and restart your PC

that can solve your problem

that happen to me a lot

Two

Update your graphics driver

outdated graphics driver also can cause problem

Another reason

If you are starting the Unity3D game Engine for the first time

then you have log in to a Unity3D account

  you can create that account from Unity3D website

Happy Gaming

This issue can often happen when your graphics driver not working properly. Here are some ways to fix your graphics driver.

One:

Because of hibernating your PC for long time sometimes the graphics driver won't work. Try to fix this by restarting or shutting down your computer.

Two:

Try updating your graphics driver from the the driver company’s website or from Windows Update.

Three:

If you are starting the Unity up for the first time, you need to log into an account first. If you don’t have one you can create one here.