Inspiron N5050 Doesnt boot up from Start or Restart Properly

Hi..

Just started happening today, Laptop starts up as normal with Dell screen, then switches to Windows blue icon with circling dots for booting up... Then just goes to black screen.......No keys responsive...Fan still running...hdd still running..

I have to hold the power button down to switch it off then reboot again... sometimes takes 5/6 attempts..

I have ran a diagnostic as it still lets you enter F2/F8 % F12 with no problems..... But still does not restart or reboot 

I have restored it to previous points.....I have now upgraded to windows 10 thinking it may be software related....

But it still happens on start up where it takes 5/6 attempts..

When the laptop is running , the screen stays on without any problem...goes into sleep and wakes without problem...

Its only when it is initially turned on or has to restart for updates i have a problem..

Would appreciate an help...