Windows 8 Welcome screen issues

Question

Windows

When you turn on the laptop for the second time on the welcome screen, one half is black (right). But after logging in, everything becomes normal. What could have caused this? Or is it just that the system is not fully loaded?
UPD: something like this

PS: I did it in Paint, but the meaning is almost the same.

Answer 1

It is possible that a curve assembly of Windows is installed.