Slow Boot up After Windows 10 upgrade

Guys

After I upgraded my operating system from Windows 8.1 to Windows 10 through Media Creation Tool, I'm experiencing quite slower boot up than it was before when I had Windows 8.1.

I have a Lenovo Y50-70 High Performance Gaming Laptop. After I press the Power button, Lenovo logo screen shows up with little balls revolving in a circle which lasts upto 10-15 seconds. Past this screen, I get Black screen with again little balls revolving (but I get the mouse cursor showed up) and it takes 2-30 seconds, and then I get the windows 10 logon welcome screen/Lock screen.

I suppose this to be very slow compared to that of Windows 8.1 which would take total 20 seconds to get lock screen.

Question is:

1) Why am I getting this black screen everytime I start my computer?
2) Can this be due to my Discrete Graphics conflict with Intel Graphics at Windows 10 startup?
3) If it is due to my Discrete Graphics conflict, then what is the possible solution for it?
4) Do I have any other alternative rather than disabling my Discrete Graphics because I need it for Gaming, otherwise there is no use of having it?

Awaiting for replies.....

Hi,Many people experiencied this kind of issue when upgrading to.The delay you get before the logon screen shows up is probably due to a driver problem!Try to upgrade your drivers. Especially the graphic card and the network drivers. But try to upgrade whatever you can ...

Thanks for a quick reply @ zinou

I forgot to write in my Previous Post that all my drivers are up-to-date, last checked 28/07/2017. Graphics Drivers and LAN & WLAN drivers are up-to-date as well, last checked 28/07/2017.

In fact, I have upgraded every driver I could upgrade to the latest version. Still the problem exists, I'm unable to find a correct solution to the problem that why is this occuring in Windows 10 as other versions of windows have never shown this...