I also reinstalled the whole system with the Win 8.1 Function into the factory settings
That should always be the very last resort option because (1) it often does not fix anything - especially with hardware issues, (2) it puts you months, if not years behind in security updates, and (3) you don't learn anything to prevent recurrence of the problem.
Much of what you describe is actually normal behavior. It is not until way into the boot process when the boot drive is finally accessed and Windows starts to load when the drivers are finally loaded for the various hardware devices. So until the specific graphics and monitor drivers are loaded, Windows uses its own native Non PnP Monitor and graphics driver.
Computers need video during the initial stages of the boot process so at the hardware level there is set of instructions providing a basic input and output system (BIOS) to allow basic video using generic drivers all operating systems, graphics solutions and monitors can communicate with. During the boot process there is some "handshaking" going on to set up any advanced capabilities, including resolutions and digital or analog data feeds. Until the final signal and settings are established, you typically see this flashing on and off as modes are changing until the final mode is set. Again this is normal.
What is not normal is for this to be happening after the system has fully booted. So you have a problem, but it is not with Windows (so Windows did not need to be reinstalled
). Your problem is either your monitor is losing sync with your graphics solution, or your graphics solution is losing sync with your monitor. And making sure the "graphics" drivers were current would be the first step.
If this were a PC, I would suggest you make sure the cable connections are tight and secure and if using a graphics card (and not integrated graphics) make sure the card is secured in its slot. Then I would suggest you swap monitors to see if the problem happens with the second monitor too.
But since this is a notebook, you cannot swap monitors but you can attach an external monitor and I recommend you do that. Note that most recent TVs support computer inputs. Use the necessary Fn + F-key combination for your notebook to switch video output to both the notebook and external monitor then see what happens.
If both the notebook monitor and external monitor blink out minutes after the system has fully booted, then you know the graphics solution in your notebook is failing. If technically able, you can disassemble the notebook to make sure the cable monitor cable is securely fastened and not being pinched somewhere. If not, then this should be left up to an experienced technician. If the cable is secure and not pinched or damaged, then sadly, being a notebook, besides updating drivers, there's not much you can do but replace the notebook.
If the external monitor does not exhibit these problems, then you know the display panel in your notebook is failing and those can be replaced.
Please note I am assuming your notebook is not full of heat-trapping dust, the fans spin properly and it is clean of malware too.
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It is also important to understand that monitor drivers are not really "drivers" per say. This is because operating systems don't really communicate directly with monitors. Operating systems communicate with the graphics solution (card or integrated graphics) and it is then the graphics solution's job to communicate with the monitor.
The primary function of the so-called monitor drivers is simply to tell Windows the brand and model number of the monitor and to gray out the non-supported resolutions. In other words, we really don't need monitor drivers at all. If your monitor has a supported feature (portrait mode, for example) your graphics card will support it.
So if ever you see a monitor maker (routers too) say you MUST install their software, they are lying! The good monitor (and router) makers are just trying to make things easier for you. Though many (including me) would say how is adding more steps to the installation process easier? But some makers of these products only want to foist extra junk (trial software, etc. ) on your system so they can get extra revenue.
Note too that some may claim the EDID (extended display identification data) is provided via the driver, that is not true. The EDID is information stored in the monitor's firmware and this information is exchanged with the graphics solution, not the OS. See
Understanding EDID for more information.
Some [so-called] monitor drivers also provide the capability to adjust color parameters via a control panel applet. But that is NOT a driver feature and these adjustments can also be done via the OSD (on-screen display) menu directly from the monitor.
