Blinking monitor while in windows, software problem.

Hello, I have a problem with my laptop, its blinking while the windows is working. But it stops when you open the Ctrl+Alt+Del menu. What is happening, its so annoying. And I can't find a reason to do it, 2 days ago I reinstall the windows, because of I m selling it and on the second day started to blinking, only when is windows working, please if someone had a solution on this problem, please share it.