Bit the bullet and upgraded my Dell Vostro 3550 to Windows 10 (even though it shows as not compatible on the Dell website)..
All seemed to be going fine - Windows 10 logo on bootup, but then the screen went black - the backlight was on, so it seemed like Windows was running but no displaying on the laptop screen.
A quick search showed it was a common problem, and that the basically the graphics card is treating the laptop screen as another monitor, and displaying the main display on the external display (that isn't plugged in!)
Connected up a monitor via a VGA cable, and the Windows 10 logon screen was displayed. Logged in and uninstalled the Intel HD 3000 Graphics card, and then let Windows download the latest driver from Windows Update.
Have also fixed a Dell Inspiron which had the same problem, but upgrading the graphics drivers didn't resolve the issue. Upgraded the BIOS as well as it was on a old version, and laptop screen worked as it should after a reboot.
