Bummer.
The flashing is likely caused by a driver, app, or device not being compatible with the Windows update.
Press Ctrl + Alt + Delete to open Task Manager. If you don’t see Task Manager after pressing Ctrl + Alt + Delete, press Ctrl + Shift + Esc to open Task Manager.
If Task Manager flickers along with everything else on the screen, a display driver is probably causing the problem. In this scenario, see https://support.microsoft.com/en-us/help/12374/windows-10-troubleshoot-screen-flickering
If Task Manager doesn’t flicker while the rest of the screen is flickering, an incompatible app is probably causing the problem. In this scenario, see https://support.microsoft.com/en-us/help/12374/windows-10-troubleshoot-screen-flickering